Source: AMERICAN ELECTRICIANS’ HANDBOOK
DIVISION 10
ELECTRIC LIGHTING
Principles and Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Electric-Light Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Incandescent (Filament) Lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Fluorescent Lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
High-Intensity-Discharge Lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Light-Emitting Diodes (LEDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Neon Lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Ultraviolet-Light Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Infrared Heating Lamps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Luminaires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Principles of Lighting-Installation Design . . . . . . . . . . . . . . . . . . . . . . .
Tables for Interior Illumination Design . . . . . . . . . . . . . . . . . . . . . . . . . .
Interior-Lighting Suggestions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Heat with Light for Building Spaces . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Street Lighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Floodlighting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10.1
10.23
10.24
10.38
10.59
10.75
10.75
10.82
10.85
10.86
10.106
10.124
10.144
10.148
10.151
10.155
PRINCIPLES AND UNITS
1. Explanation of light. For the principal purposes of illumination design, light
(Standard Handbook for Electrical Engineers) is defined as visually evaluated radiant
energy. The visible energy radiated by light source is found in a narrow band in the electromagnetic spectrum, approximately from 380 to 770 nanometers (nm). Figure 10.1 shows
the complete radiant-energy spectrum of electromagnetic waves, which travel through
space at the velocity of approximately 3.0 108 m/s (186,000 mi/s). The longer waves are
the ones used in radio communications; the shortest ones are the x-rays and cosmic rays.
An enlarged section of the visible light portion of the spectrum is shown in the figure.
The effect of light upon the eye gives us the sensation of sight. The impression of color
depends upon the wavelength of the light falling upon the eye. There are three primary
colors of light: red, green, and violet. Violet light has the shortest wavelength of the radiant
energy to which the eye is sensitive, red the longest, and green an intermediate wavelength
between those of violet and red. These three colors are called the primary colors, because
light of any one of them cannot be produced by combining light of any other colors. Light
of any other color than these three can be produced by combining in the proper proportions
light of two or all three of the primary colors.
By extension, the art and science of illumination also include the applications of ultraviolet and infrared radiation. The principles of measurement, methods of control, and fundamentals of lighting system and equipment design in these fields are closely parallel to
those long established in lighting practice.
10.1
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ELECTRIC LIGHTING
10.2
FIGURE 10.1
DIVISION TEN
The electromagnetic spectrum.
2. Propagation of light. Rays of light travel in straight lines unless interfered by
some medium that absorbs or deflects them. Whenever a light wave strikes a different
medium from that through which it has been passing, there are three fundamental phenomena that may occur: absorption, reflection, or refraction. Whenever light waves strike any
object, a portion of their energy is absorbed, the amount depending upon the nature of the
substance. This absorbed energy is dissipated in the form of heat. The remaining portion of
the light may be all transmitted through the substance, all reflected back from the surface,
or part transmitted and part reflected, depending upon the nature of the substance and the angle
at which the light impinges upon the surface of the object. If the light strikes the object perpendicularly to the surface, it is either transmitted in a straight line through the substance
or reflected back from its surface in the same direction in which it impinged upon the surface. If light strikes an object at an angle other than 90 to its surface, then either the light
is transmitted through the object but in an altered direction (refraction) or the light is
reflected back from the object but in a different direction from that in which it impinged
upon the object (reflection). With most objects all three of the phenomena occur, some of
the light impinging upon them being absorbed, some transmitted through (refracted), and
some reflected back from the surface.
3. Absorption. Although some of the energy of a ray of light is always absorbed
whenever a light ray impinges upon an object, the amount absorbed varies over wide limits, depending upon the nature of the object, the molecular construction, the wavelength or
color of the incident light, and the angle at which the light strikes the surface. All objects
do not absorb light of different wavelengths in the same proportion. It is this phenomenon
which accounts for the characteristic color of objects (see Sec. 13). Since objects do not
absorb the same proportion of the incident light of different colors, the amount of light
absorbed by an object depends upon the color or wavelength of the light impinging upon
the object. Tables 4 and 12 give the percentage of incident white light that is absorbed by
various types of surfaces.
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ELECTRIC LIGHTING
10.3
ELECTRIC LIGHTING
4. Coefficients (Percent) of Absorption of Lighting Materials
Material
Absorption, percent
Clear glass globes
Light sandblasted globes
Alabaster globes
Canary-colored globes
Light-blue alabaster globes
Heavy blue alabaster globes
Ribbed glass globes
Clear plastic globes
Opaline glass globes
Ground-glass globes
Medium opalescent globes
Amber glass
Heavy opalescent globes
Flame-glass globes
Enameled glass
White diffuse plastic
Signal-green globes
Ruby-glass globes
Cobalt-blue globes
5–12
10–20
10–20
15–20
15–25
15–30
15–30
20–40
15–40
20–30
25–40
40–60
30–60
30–60
60–70
65–90
80–90
85–90
90–95
5. Absorptance. (Standard Handbook for Electrical Engineers) given the alpha
symbol “” in engineering work, is the ratio of the flux absorbed by a medium to the incident flux. Transmittance, given the tau symbol “” in engineering work, is the ratio of the
transmitted flux to the incident flux. Measured values of transmittance depend upon the
angle of incidence, the method of measurement of the transmitted flux, and the spectral
character of the incident flux. Because of this dependence, complete information of
the technique and conditions of measurement should be specified. The sum of reflectance
(Sec. 8), transmittance, and absorptance is one.
6. Reflection of light. (Fig. 10.2) is the redirecting of light rays by a reflecting surface. Whenever light energy strikes an opaque object or surface, part is absorbed by the surface and part is reflected. Light-colored surfaces reflect (Table 9) a larger part of the light
thrown on them than do dark-colored surfaces, whereas dark surfaces absorb a larger part
of the light and black surfaces absorb nearly all the light which reaches them.
NOTE Consider first a smooth surface AB (Fig. 10.2, I), on which a ray of light L falls.
This ray will be so reflected in the direction R that the angle i is exactly equal to the angle r.
FIGURE 10.2
reflection r.
The reflection of light. Note that the angle of incidence i always equals the angle of
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ELECTRIC LIGHTING
10.4
DIVISION TEN
Consider now the effect of a number of rays falling on a smooth surface CD (Fig. 10.2, II).
Each ray will be reflected in such a way that it leaves the surface at the same angle at
which it strikes. The eye if held as shown would perceive only the light reflected into it.
Consider now a broken surface such as FG (Fig. 10.2, III). Each ray of light is reflected
from that portion of the surface on which it falls, just as though that point were on a smooth
surface. The result is that the light is scattered, and if the surface is irregular enough, the
eye placed at any point will receive reflections from many points of the surface. All opaque
surfaces except polished surfaces have innumerable minute irregularities like the surface in
Fig. 10.2, III. This alone enables them to be seen.
7. The different kinds of reflection will now be considered. Regular reflection is
that (Fig. 10.3A, I, and 10.3B, I) in which the angle of incidence i is equal to the angle of
reflection r. This kind of reflection is obtained from mirrored glass, prismatic glass, and
polished metal surfaces. Spread reflection (Fig. 10.3A, II, and 10.3 B, II) is that in which
the maximum intensity of the reflected light follows the law of regular reflection, except
that a part of the light is scattered slightly out of this line. Spread reflection is obtained from
etched prismatic glass and from rough metallic surfaces. Diffuse reflection (Fig. 10.3 A, III)
is that in which the maximum intensity of the reflected light is normal to the reflecting
surface. This holds over a large range of the angle of incidence. This kind of reflection is
usually caused by reflection from particles beneath the surface (see Fig. 10.3B, III). Diffuse
reflection may be obtained from opal glass, porcelain enamel, paint enamel, and paint finishes
commonly used for interior decoration of walls and ceilings.
FIGURE 10.3A
Classifications of reflection.
FIGURE 10.3B
Magnified view of Fig. 10.3A.
8. Reflecting power of surfaces. (Standard Handbook for Electrical Engineers)
Different surfaces reflect different percentages of the light falling upon them. Reflectance,
given the rho symbol “” in engineering work, is the ratio of reflected flux to incident flux.
Measured values of reflectance depend upon the angles of incidence and view, and on the
spectral character of the incident flux. Because of the dependence, the angles of incidence
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ELECTRIC LIGHTING
10.5
ELECTRIC LIGHTING
and view and this spectral characteristics of the source should be specified. The illumination of a small room having poorly reflecting walls may sometimes be improved by changing the wall coverings. If the room is large or if reflectors are used to throw the light
downward so that not much light reaches the walls, a change in the wall covering will have
little effect on the general illumination.
9. The following table of reflection coefficients is useful in showing the relative
value of wall coverings in rooms.
Material
Highly polished silver
White plaster
White paint
Optical mirrors silvered on surface
Highly polished brass
Highly polished copper
Highly polished steel
Speculum metal
Limestone
Brushed aluminum
Polished gold
Burnished copper
White paper
Porcelain enamel
Polished aluminum
Chrome-yellow paper
Yellow paper
Light-pink paper
Blue paper
Dark-brown paper
Vermilion paper
Blue-green paper
Cobalt blue
Glossy black paper
Deep chocolate paper
Black cloth
Reflection, %
92
90
75–90
75–85
70–75
60–70
60
60–80
35–65
55
50–55
40–50
80
70–80
67
62
40
36
25
13
12
12
12
5
4
1.2
10. Refraction. Whenever a light ray passes from one medium into another of greater
or less density, the direction of the ray is altered. This is called refraction. Refraction may
be one of three types: regular, irregular or spread, or diffuse, depending upon the nature of
the construction of the substance and the character of its surfaces.
Regular refraction occurs with plain glass
or glass prisms, as shown in Fig. 10.4. Light in
passing through a substance goes through two
refractions, one upon entering the substance
and one upon leaving the substance. If the surfaces of the object are parallel, as in a piece of
glass (Fig. 10.4, I), the direction of the light
leaving the object is parallel to the direction of
the light impinging upon the object. If the FIGURE 10.4 Regular refraction.
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ELECTRIC LIGHTING
10.6
DIVISION TEN
surfaces of the object are not parallel, as in the prism of Fig. 10.4, II, the light leaving the
object will not be in a direction parallel to the incident light. A prism can be constructed to
refract the light from its different surfaces so that light is not transmitted through the prism
but is reflected back as shown in Fig. 10.5.
Irregular, or spread, refraction occurs with light transmitted through glass with a rough
surface such as etched or frosted glass, as shown in Fig. 10.6. Such a surface can be considered as consisting of a great number of very small smooth surfaces making slight angles
with each other. The individual rays of light being emitted from such a surface are refracted
at slightly different angles but all in the same general direction. Thus the light transmitted
through a substance with such a surface is refracted in the same general direction but with
the beam spread somewhat from what would be for regular refraction.
FIGURE 10.5 Total reflection
prism. [General Electric Co.]
with
FIGURE 10.6 Spread refraction with
etched glass. [General Electric Co.]
The composition of opal glass is such that it contains a number of minute opaque particles throughout its structure. Light striking such an object travels through the glass until it
strikes one of these opaque particles, from which it is either reflected back or transmitted
through the glass to the other surface. The total beam of light striking the object is thus split
up by the innumerable small opaque particles, part being reflected back in all directions,
and part being refracted through the glass in all directions. The portion that is transmitted
(refracted) through the glass is diffusely refracted. An idea of how diffuse refraction takes
place can be gained from Fig. 10.7. In Fig. 10.8 the diffuse reflection and refraction of a ray
of light impinging upon a piece of opal glass are indicated.
FIGURE 10.7 Diffuse refraction.
FIGURE 10.8 Diffuse reflection
and refraction with opal glass.
[General Electric Co.]
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ELECTRIC LIGHTING
11. Most Frequently Used Lighting Units, Abbreviations, and Symbols and
the Corresponding Hydraulic Analogies
Photometric quantity
Name of unit
Abbreviation
Symbol
Hydraulic analogy
Luminous flux
Luminous intensity
Illuminance
Luminance
lumen
candela
footcandle
lambert
lm
cd
fc
lambert
F
I
E
L
gal/min
pressure, lbf/in2
incident gal/(ft2min)
issuing gal/(ft2min)
12. Refraction, Transmission, and Absorption Characteristics of Materials
(General Electric Co.)
Material
Crystal glass:
Clear
Frosted or pebbledb
Frosted or pebbledc
White glass:
Very light densityb
Very light densityc
Heavy density
Mirrored glass
Polished metal:
Silver
Chromium
Aluminum
Alsak aluminum
Nickel
Tin
Steel
Porcelain enamel steel
Mat-finished metal:
Aluminum
White oxidised
aluminum
Aluminum paint
Mat surfaces:
White plaster
White blotting paper
White paper
(calendered)
White paint (dull)
White paint (semimat)
White paint (gloss)
Black paint (gloss)
Black paint (dull)
Magnesium carbonate
Plastic:
Clear
White diffuse
Light reflected
Light transmitted
In
In
Diffused
concentrated spread
in all
beam
beam directions
In
In
Diffused
concentrated spread
in all
beam
beam directions
Light
absorbed
8–10a
4–5
.....
.....
5–10
8–12
.....
.....
.....
80–85
.....
.....
.....
70–85
72–87
.....
.....
.....
5–10
5–15
5–15
4–5a
.....
4–5a
82–88
.....
3–4
.....
.....
10–20
10–20
40–70
.....
5–20
.....
.....
.....
.....
5–20
.....
.....
50–55
50–55
10–45
.....
8–12
10–15
10–20
12–18
92
65
62
75–85
55
63
60
4–5a
.....
.....
.....
70–80
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
60–70
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
8
35
38
15–30
45
37
40
25–35
.....
.....
62
70–75
.....
.....
.....
.....
.....
.....
.....
.....
38
25–30
.....
60–65
.....
.....
.....
.....
35–40
.....
.....
4–5a
.....
.....
.....
90–95
80–85
75–80
.....
.....
.....
.....
.....
.....
.....
.....
.....
5–10
15–20
15–20
.....
.....
4–5a
4–5a
.....
.....
.....
2–4
.....
.....
.....
.....
75–80
70–75
70–75
3–5
3–5
98–99
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
.....
20–25
20–25
20–25
85–92
95–97
1–2
.....
.....
.....
.....
.....
.....
.....
.....
60–80
.....
.....
5–35
40–20
65–95
a
For angles up to 45; for angles greater than 45, this value rises considerably; angle of incidence as X, Fig. 10.6.
Smooth side toward light source.
Roughed on side toward light source.
b
c
10.7
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ELECTRIC LIGHTING
10.8
DIVISION TEN
13. Color of objects. Our impression of the color of objects is due to the color of the
light that the object reflects or transmits to our eyes. In Sec. 2 it was stated that all objects
absorb a certain portion of the light that falls upon them but that all objects do not absorb
the same proportion of light of the different wavelengths. It is through this different
absorption that different objects have unlike colors. If all objects absorbed light in exactly
the same manner, all objects would appear to have the same color. In order that things may
appear in their true colors, they must be observed under white light, that is, light containing all three primary colors in the right proportion. An article which absorbs no light or
which absorbs light of the three primary colors in the same proportion as they are combined to produce white light will transmit from its surface light in a condition unchanged
from that in which the light fell upon the object. Such an object would appear white in
color. An object which absorbs all or nearly all the light which falls upon it will have no
color or, in other words, will be black. An object which absorbs all the green and violet
rays will be red in color, since it will transmit to our eyes only red light. In order that an
object may appear in its true color, the light falling upon it must contain light of the wavelength that the object reflects or transmits. Thus, light falling upon a red object must contain red light if the object is to appear in its true color. A red object viewed under a light
which contains only green and violet rays will appear black, since the object is capable of
reflecting only red rays.
14. Light-source color. The color of light sources has two basic characteristics:
chromaticity and color rendering. Chromaticity, or color temperature, defines its
“whiteness,” its blueness or yellowness, its warmth or coolness. It does not describe
how colors will appear when lighted by the source. Chromaticity (color temperature) is
a term sometimes used to describe the color of the light from a source by comparing it
with the color of a blackbody, a theoretical complete radiator which absorbs all radiation that falls on it and in turn radiates a maximum amount of energy in all parts of the
spectrum. A blackbody, like any other incandescent body, changes color as its temperature is raised. The light from a warm white fluorescent lamp is similar in color to the
light from a blackbody at a temperature of approximately 3000 K,* and the lamp is
accordingly said to have a color temperature of 3000 K. The light from a cool white fluorescent lamp is bluer, and the blackbody must be raised to 4200 K to match it. Hence
the cool white lamp has a color temperature of 4200 K. A daylight fluorescent lamp has
a color temperature of 6200 K.
Color temperature is not a measure of the actual temperature of an object. It defines
color only. Some light sources, such as a sodium-vapor lamp or a green or pink fluorescent
lamp, will not match the color of a blackbody at any temperature, and therefore no color
temperatures can be assigned to them.
*Kelvin is a temperature scale which has its zero point at 273C.
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ELECTRIC LIGHTING
10.9
ELECTRIC LIGHTING
Color Temperatures, K
(Approximate values)
Blue sky
Overcast sky
Noon sunlight
Fluorescent lamps
Daylight
Cool white
White
Warm white
Clear mercury lamps
Deluxe mercury lamps
Clear metal halide lamps
High-pressure sodium lamps
General-service incandescent lamps
Candle flame
10,000–30,000
7000
5250
6200
4200
3500
3000
5700
3900
4100
2100
2500–3050
1800
The other characteristic, the color-rendering index (CRI), attempts to describe how colors will appear when illuminated by a light source of specified chromaticity. The CRI rating system is an international system that mathematically compares how a light source
causes eight selected colors to appear compared with a reference source. However, there
are limitations to its use which should be recognized. Although the system provides for ratings up to 100, it can only be used to compare sources of approximately the same chromaticity. Comparison of the CRI of light sources with widely different color temperatures
such as a cool light source and a warm light source can be misleading. Light sources with
the same CRI may render some colors differently, and light sources with CRIs as much as
5 points different may cause colors to look the same. Owing to their spectral distribution,
HID sources may actually look better than their CRIs would indicate.
The CRI system is the best presently available to describe the relative appearance of
colors under different sources, and it can be useful when applied within the limits of the
system.
15. Luminous flux (which, as is explained later, is measured in lumens) is a flow of
light, that is, light energy or light waves. Luminous flux always originates from some
source of light, such as the sun, a candle, or an incandescent lamp. But luminous flux can
be redirected by reflecting surfaces. The luminous flux which emanates directly or is
reflected from objects to the human eye is the medium whereby the objects are seen.
Although there is no actual flow of anything material in a flux of light, there is a flow of
light waves. The formal definition (Standard Handbook for Electrical Engineers) is that
luminous flux is the integrated product of the energy per unit wavelength emitted by the
source P(), referred to as the source’s spectral power distribution, and the spectral luminous efficacy V() as follows:
800
683 3 P(l)V(l)dl
l 360
From this it can be seen that the maximum possible output of a light source is 683 lm/W.
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ELECTRIC LIGHTING
10.10
DIVISION TEN
16. A true point source of light is a luminous mathematical point which emits
luminous flux uniformly in all directions. It is a theoretical concept which cannot actually
exist. It is, however, used (and is necessary) for the development of the quantities and units
employed in lighting computations.
NOTE An actual light source may be considered a point source without prohibitive error
if the distance between the source and the location at which the source is viewed or examined is at least 10 times the greatest dimension of the source.
FIGURE 10.9 A steradiahn illustrated. It
is, in effect, the flare angle of a cone that,
when striking the surface of a cone at any
distance, cuts off an area (shown crosshatched in the figure) equal to the square of
the distance. In the case of a projected beam
of light, the number of steradians equals
the projected area divided by the distance
squared A steradian covers about one-twelfth
of the area of the entire sphere.
17. The luminous intensity (candlepower) of a given source of light in a certain
specified direction is a measure of the ability of
the source to project light in that direction.
Luminous intensity is measured in a unit which is
called the candela, formerly the candle. Fig. 10.9
(Practical Electrical Wiring, 20th edition, © Park
Publishing, 2008, all rights reserved) illustrates
the term “steradian” which is necessary to the
definition of this and other fundamental lighting
terms. If a light source emits 1 lumen of light, and
that light is directed within 1 steradian of solid
angle, that light source has a luminous intensity of
1 candlepower.
NOTE The luminous intensity of actual light
sources is generally greater in certain directions
than in others. Thus, in Fig. 10.10, the luminous
intensity of the lamp is greatest in the horizontal
direction.
FIGURE 10.10 Luminous intensities in different directions around an
incandescent lamp.
18. The candela (cd) was formerly defined as the luminous intensity or lightproducing power in the horizontal direction of a standard lamp which is made and used in
accordance with U.S. Bureau of Standards specifications.
NOTE The luminous intensity of an ordinary sperm candle (Fig. 10.11) in the horizontal direction is about 1 candle (cd). Thus was derived the name of the unit, candela.
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
FIGURE 10.11
(10.76 lx).
10.11
An intensity of illumination of 1 fc
19. The true luminous intensity or candlepower of a light source can be
obtained only when the source is a true point source (Sec. 16). But a true point source does
not exist. It is merely a mathematical concept. Now, the luminous intensity of an actual
light source, in a certain direction (Fig. 10.12), is due to the combined effects of a number
of point sources in the surface of the actual light source. Hence, the luminous intensity of an
actual light source, in a given direction, as determined with a photometer (Sec. 27), is not
the true candlepower (luminous intensity) but is the apparent luminous intensity (apparent
candlepower) in that direction.
FIGURE 10.12 The illumination at point S is due to the combined effects of an infinite number of point sources P1, P2, P3, etc.
20. Illuminance is measured in footcandles (fc) or lux (lx). The footcandle is
defined as that illumination which is produced (Fig. 10.11) by a 1-cd point source (or its
equivalent) on a surface which is exactly 1 ft (0.3048 m) distant from the point source. The
lux is the illumination produced by a 1 cd point source at a distance of 1.0 m from the
source.
EXPLANATION If, in Fig. 10.11, the light source S is assumed to be a point source of
luminous flux, then the illumination at point A, which is exactly 1 ft from S, is (by definition) 1 fc. Since the illuminated surface MNOP is a plane, point A is the only point on the
surface which has an illumination of 1 fc. The illumination at any other point on the surface,
such as B or C, is less than 1 fc because it is farther away from S than is A. If, however, the
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ELECTRIC LIGHTING
10.12
DIVISION TEN
sphere of Fig. 10.9 has an internal radius of 1 ft and the true point source (Sec. 16) has a
luminous intensity of 1 cd, then every point on the interior surface of the sphere will have
an illumination of 1 fc (10.76 lx).
21. Illuminance is really the density of the luminous flux which impinges on
the surface of an illuminated object. The average density of anything on a surface may be
numerically represented by the number of things on the whole surface divided by the number of unit areas in the surface. Thus, as will be further explained in Sec. 25, if the luminous flux, in lumens, which impinges on a surface, is divided by the area of that surface in
square feet, the average illumination over the surface will be the result.
22. Luminous flux is measured in lumens (lm). A lumen is defined as that quantity of incident luminous flux which will, when uniformly distributed over a surface having an area of 1 ft2 (0.0929 m2), produce an illumination of 1 fc on every point of the
surface. It will also illuminate a surface of 1 m2 to a level of 1 lux.
When luminous flux impinges nonuniformly on a surface, then a lumen is the
NOTE
quantity of luminous flux which will, on a 1-ft2 area of the surface, produce an average
illumination of 1 fc.
23. A point source of light of 1-cd luminous intensity emits 12.57 lm. It has
been shown (Sec. 20 and Fig. 10.9) that a 1-cd point source of light located at the center of
a hollow sphere of 1-ft radius will produce an illumination of 1 fc on every point of the interior surface of the sphere. Now the superficial area of a sphere 4
r 2 4 3.1416 r 2.
Hence, this 1-ft-radius sphere will have an area of
4 3.1416 1 1 12.57 ft2
Since every point on the surface of this sphere has an illumination of 1 fc, there must,
to satisfy the definition of the lumen (Sec. 22), be as many lumens emitted by the 1-cd point
source as there are square feet in the surface of the sphere. The sphere has an area of 12.57 ft2.
Therefore every 1-cd point source of light emits 12.57 lm.
24. To obtain the output of a light source in lumens when its mean sphereical candlepower is known, substitute in the following formula. This formula is
strictly accurate only for a true point source (Sec. 16) of light, but it gives results sufficiently accurate for all practical purposes if the mean spherical candlepower (Sec. 29) is
substituted for I.
F 12.57 I lm
(2)
where F total luminous flux emitted by the light source, in lumens, and I luminous
intensity or candlepower of a point source, in candelas, or, with sufficient accuracy for most
practical purposes, the mean spherical candlepower of an actual light source.
The mean spherical candlepower of a light source is 68.8. What quantity of
luminous flux is emitted in lumens?
EXAMPLE
SOLUTION
By For. (2), luminous flux F 12.57 I 12.57 68.8 865 lm.
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.13
25. Illuminance in footcandles is really lumens per square foot. From the definition of the lumen in Sec. 22, 1 lm of flux spread out over an area of 1 ft2 produces 1 fc
average illuminance over that surface; 2 lm would produce 2 fc, etc.
Similarly, 10 lm spread out over an area of 5 ft2 would produce an average illuminance
of 10 5 2 fc. Likewise, 1 lm spread out over an area of 2 ft2 would produce an illuminance of 1 2 0.5 fc. Thus, it is evident that lumens ft2 area average footcandles
illuminance.
A room which has an area of 600 ft2 has 3300 lm of luminous flux impinging
on the working plane. What is the average illuminance, in footcandles, on the working
plane?
EXAMPLE
By the equation given above, average footcandles illumination lumens ft2 area 3300 600 5.5 fc.
SOLUTION
26. The illuminance, in footcandles, which from a light source impinges on
a surface, varies inversely as the square of the distance from the source. This
is true absolutely for a true point source (Sec. 16). It is approximately true if the distance is
at least 10 times the largest dimension of the light source.
EXPLANATION Assume (Fig. 10.13) that the 1-cd point source P is placed at the center
of a hollow spherical shell which has an internal radius D of 1 ft. Then, a section A of the
shell, having an area of 1 ft2, will have on its inner surface an illumination of 1 fc. This follows from the preceding discussions. Furthermore, from the definition of the lumen (Sec. 22),
just 1 lm of flux is lighting this surface. Now, if the 1-ft-radius sphere is removed and the
1-cd source be placed at the center of a 2-ft-radius sphere, i.e., one of double the radius,
then the same luminous flux will be spread out over an area B of 4 ft2. (This follows because
of the geometric fact that similar areas vary directly as the square of similar dimensions.)
The illumination on B will be 1 lm 4 ft2 0.25 fc. Thus by doubling the distance from
the source, the illumination has been quartered. Similarly, it can be shown for C that with the
distance D increased 3 times the illumination provided by 1 lm of flux is one-ninth of what
it was with the distance of 1 ft. Thus, illumination varies inversely as the square of the
distance from the source.
FIGURE 10.13
The inverse-square law.
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ELECTRIC LIGHTING
10.14
DIVISION TEN
27. The photometer is an instrument which is used for determining the luminous
intensity of a light source. Any determination made with a photometer gives apparent
candlepower. However (Sec. 26), if the location at which the intensity is measured is at
a sufficient distance from the source, then the source may for all practical purposes be considered a point source, and the value obtained for the unknown candlepower will be accurate well within the limits of error of experimental observation.
Photometric measurements are obtained from visual comparison of an unknown light
source compared with a known source or with direct-reading photoelectric instruments
which have been calibrated from a known source. The latter method is the most widely used
today in the measurement of lamps and lighting fixtures.
28. Mean horizontal candlepower is the average of the candlepowers of a lamp
in all directions in a horizontal plane. This term is now applied only to special lamps for
laboratory test work.
29. Mean spherical candlepower is the average of the candlepowers of a lamp in
all directions. It is measured by putting the lamp in the center of a sphere photometer
(Fig. 10.14). The sphere has a small window of milk glass which is shielded from the direct
rays of the lamp by a small opaque screen. The inner surface of the sphere is painted flat
white for good reflection of the light. The candlepower of the window is compared with the
horizontal candlepower of a standard lamp. This candlepower must be multiplied by a constant for the particular sphere to take account of the loss of light absorbed on the inner surface of the sphere and in the glass window. The mean spherical candlepower is used
principally with the equation of Sec. 24 to obtain the lumen output in which the lamp is rated.
FIGURE 10.14
Sphere photometer. [General Electric Co.]
30. The luminous efficacy (also referred to as efficiency) of an electric-light
source is stated in lumens per watt. This term is obtained by dividing the lumen output of
the source by the watts input. It is (Standard Handbook for Electrical Engineers) the ratio
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.15
of the total luminous flux (lumens) to the total power input (watts). The maximum luminous efficacy of an ideal white source, defined as a radiator with constant output over the
visible spectrum, is approximately 200 lm/W.
31. Candlepower distribution curves. Since the common light-giving sources
either alone or in conjunction with the reflecting equipment used with them do not have the
same light-giving power or candlepower in all directions, photometric graphs are employed
to indicate the candlepower of the source in all directions. Curves giving this information
for a light source are called candlepower distribution curves or simply distribution curves.
These curves are obtained from a photometer which measures the luminous intensity of a
light source in all directions (Fig. 10.15).
FIGURE 10.15 Mirror photometer used to measure the luminous
intensity of a light source or luminaire in all directions. [General
Electric Co.]
Many lamps or lamps with their reflectors have the same candlepower in all directions
in any one horizontal plane. This fact enables the candlepower in any direction from such
a source to be determined from a single distribution curve which gives the candlepowers in
all directions in a vertical plane through the center of the light source.
32. How to read a photometric graph. In the photometric graph of Fig. 10.16, I,
the candlepower directly downward is indicated by measuring it off on the vertical to a
given scale. Thus, XA represents the candlepower directly below the light. Similarly, the
distances XB, XC, XD, XE, XF, and XG represent to scale candle-powers around the light
at angles above the vertical of 15, 30, 45, 60, 75, and 90. Similarly, the candlepowers
above 90 can be measured off to the given scale along lines at their respective angles.
These points are then joined by a continuous line GFED, etc., and this line, completed for
360, is called the photometric distribution graph of the light source. Figure 10.16, I,
shows such a completed photometric curve, but in practice it is customary to use circular lines, as indicated on Fig. 10.16, II, to show the scale to which the candlepowers are
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ELECTRIC LIGHTING
10.16
FIGURE 10.16
DIVISION TEN
Photometric graphs.
plotted. The candlepower of the light unit can be measured at as few or as many angles
as necessary, the accuracy of the resultant graph being largely determined by the number
of angles taken.
33. The area of the distribution graph is not proportional to the amount of
light given off. B (Fig. 10.78) represents a smaller total flux, by an amount equal to the
absorption in the reflector, than does Graph A, though it has a larger area. Such a graph as
B is useful for determining the intensity of light at any given angle and for determining the
total luminous output, as explained in Sec. 34. These data may be required for any one of
a number of practical operations.
34. The method of computing from its distribution graph the total flux, in
lumens, emitted by a symmetrical light source is this: From the distribution graph of
any light unit, as Fig. 10.16, take the candlepower at 5 and multiply it by the 0-10 factor
as given in Table 36. This gives the lumens in the 0–10 zone. Similarly, to obtain the
lumens in the 10–20 zone, take the candlepower at 15 and multiply it by the 10–20
factor as given in Table 36. The total lumen emitted in any large zone is obtained by
adding the lumens of all the 10 zones contained in the large zone. If the sum total of the
lumens is thus obtained for the 0–180 zone, the result is the total flux, in lumens, emitted
by the source.
What is the total flux emitted by a light source having a distribution graph as
shown in Fig. 10.16?
EXAMPLE
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ELECTRIC LIGHTING
10.17
ELECTRIC LIGHTING
SOLUTION
Degrees
(1)
Candlepower
(2)
Zone factor
(3)
Lumens
(4)
5
15
25
35
45
55
65
75
85
95
105
115
125
135
145
155
165
175
100
98
94
84
66
46
33
27
26
26
25
24
20
15
12
8
4
4
0.095
0.283
0.463
0.628
0.774
0.897
0.992
1.058
1.091
1.091
1.058
0.992
0.897
0.774
0.628
0.463
0.283
0.095
9.50
27.45
43.50
52.75
51.10
41.25
32.71
28.55
28.37
28.37
26.48
23.80
17.94
11.60
7.54
3.70
1.13
0.38
Total 436.12
Total flux emitted 436.12 lm.
Column 2 is obtained from the graph (Fig. 10.16). Column 3 is obtained from Table 36.
Column 4 is obtained by multiplying the values in col. 2 by the corresponding values of col. 3.
NOTE The total flux in lumens emitted by a light source can be computed graphically
as follows. On the candlepower distribution graph (Fig. 10.16) measure the horizontal distance between the vertical axis (0–180 line) and the point where the candlepower graph
crosses the 5 line. Then lay off this distance on the candlepower scale to which the distribution graph is plotted. Multiply the value thus obtained by 1.1, and the result is the quantity of luminous flux, in lumens, emitted by the light source in the 0–10 zone. To determine
the flux in any 10 zone, it is only necessary to measure the horizontal distance between the
vertical axis and the point where the candlepower graph crosses the center of the 10 zone
under consideration and then proceed as above. To obtain the total lumens emitted in any
large zone lay off the horizontal distances between the vertical axis and the point where the
candlepower graph cuts the center of each 10 zone contained within the large zone successively along the edge of a strip of paper. Then lay off the total length on the candlepower
scale and multiply the result by 1.1.
For the determination of the lumen output of nonsymmetric or asymmetric luminaires,
such as conventional fluorescent units, readings of candlepower must be taken in a number
of planes. From these readings a weighted average candlepower is obtained for each zone.
For fluorescent lighting units, candlepower readings often are taken in five planes, at 0,
221/2, 45, 671/2, and 90 from a plane through the luminaire axis. Candlepower values are measured in each of these planes at 10 intervals (5, 15, 25, etc.). If the candlepower readings in
the five planes (0, 221/2, 45, 671/2, and 90) for any one zone are designated, respectively, as A,
B, C, D, and E, then their weighted average for that zone is obtained by the formula
cd A 2B 2C 2D E
8
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ELECTRIC LIGHTING
10.18
DIVISION TEN
In some laboratories for similar tests, candlepower readings are taken in three planes
only (0, 45, and 90), as in Fig. 10.17. The candlepower values in A (crosswise) and B
(lengthwise) plus twice the values in C (45) are added. The sum divided by 4 equals the
average candlepower.
Similarly, nonsymmetric or asymmetric luminaires for filament lamps have such wide
variations in candlepower at a given angle about the vertical that an average reading from
which to compute zonal lumens cannot be obtained by rotating the unit. Candlepower distribution curves for such equipment are prepared from data obtained in specific planes, and
in interpreting such curves one must be careful to observe the planes they represent (see
Fig. 10.18).
FIGURE 10.17 The average candlepower multiplied by the zone constant gives the zone lumens.
Candlepower values at a given angle in curves A
and B are added to twice the value in curve C at the
same angle. This sum is divided by 4 to get the
weighted average candlepower.
FIGURE 10.18 Candlepower distribution curves
of nonsymmetrical sources such as show-window
reflectors vary widely, and their interpretation
depends on the specific planes in which they are
taken.
35. The mean spherical candlepower (Sec. 29) of a light source can be
determined (1) directly, by means of the sphere photometer (Sec. 29 and Fig. 10.14),
and (2) indirectly, by computing the total lumens from the distribution graph, as
explained in the preceding paragraph, and dividing the result by 12.57.
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ELECTRIC LIGHTING
10.19
ELECTRIC LIGHTING
What is the mean spherical candlepower of the light source of which the distribution graph is shown in Fig. 10.16?
EXAMPLE
By the example in Sec. 34, the total flux of the source 436.12 lm. The
mean spherical candlepower 436.12 12.57 34.6.
SOLUTION
36. Factors to obtain the lumens in the 10 zones around a light source. To
obtain the lumens in any zone, multiply the candlepower at the center of the zone by the
factor for that zone.
Degree zones
0–10
10–20
20–30
30–40
40–50
50–60
60–70
70–80
80–90
Factor
170–180
160–170
150–160
140–150
130–140
120–130
110–120
100–110
90–100
0.095
0.283
0.463
0.628
0.774
0.897
0.992
1.068
1.091
37. The footcandle meter (also called the light meter or luminance meter) is an
instrument for measuring illumination directly in footcandles. It consists of one or two photovoltaic cells connected to a microammeter. When light falls on the photovoltaic cells, a
voltage is generated as current flow through the meter approximately in proportion to the
footcandle illumination on the cell. The small pocket type of footcandle meter is commonly
referred to as a light meter (Fig. 10.19). It has a single photovoltaic cell and is calibrated in
footcandles. The meter is placed with the window of the photovoltaic cell parallel to the
plane in which it is desired to measure the illumination. Higher levels of illumination (such
as those of daylight intensity) are measured via multiple scales on the same meter which
are chosen through a selector switch.
Larger and more accurate meters (Fig. 10.20) have additional cells connected in parallel
and utilize solid-state electronic circuits to amplify the output of the photovoltaic cells and
maintain excellent accuracy through a wide range of footcandle levels.
FIGURE 10.19 The light
meter. [General Electric Co.]
FIGURE 10.20 Light meter for more accurate
readings. [Minolta Corporation]
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ELECTRIC LIGHTING
10.20
DIVISION TEN
Since the spectral response of photovoltaic cells is not the same as that of the human
eye, it is necessary to incorporate filters into the light meter for the meter to read lighting
levels properly under all different light sources. Another factor that requires correction
within the meter is the proper measurement of light from various angles. If no correction is
included, light at high incident angles will be reflected off the photovoltaic-cell surfaces
with a resulting low reading of lighting level. Most footcandle meters today include a
means of correcting the meter response to include light from all angles. This is referred to
as cosine correction.
38. Glare (Fig. 10.21) is defined as any brightness within the field of vision of such a
character as to cause discomfort, annoyance, interference with vision, or eye fatigue.
NOTE Glare may be subdivided into three different classes: (1) Direct glare (Fig. 10.21, II),
which results when one looks directly at a brilliant light source. (2) Contrast glare, which
is caused by brightness contrast. An example of this is the visual discomfort produced by a
brilliant automobile headlight shining in the eyes on a dark night. The same headlight
would cause no discomfort in the daytime. The annoyance experienced at night is due
solely to the contrast between the bright headlight and the dark surroundings. (3) Reflected
glare (Fig. 10.21, I), which is produced by light being reflected directly into the eyes from
a polished, a white, or a light-colored surface. Glass desk plates, highly polished furniture,
glazed paper, and mirrors may occasion reflected glare.
FIGURE 10.21
Methods of causing glare.
39. Brightness is the property of lighted objects which enables them to be seen by
virtue of the light issuing from them. Technically, brightness is the density of luminous flux
issuing or projected from a light source or from some illuminated surface.
NOTE
The relation between brightness and illuminance: Illuminance is the density of
the luminous flux impinging on an illuminated surface. Just as illuminance measures
incident–luminous-flux density, so brightness measures issuing–luminous-flux density. It is
due solely to the light issuing or reflected from things that we see. There might be great illumination (incident–luminous-flux density) on a dead-black object in a room with deadblack walls, and yet that object would be invisible, because the black would absorb (see
Table 9) all the light which impinged on it and would reflect none to the eye.
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.21
40. The units of brightness are the lambert, the millilambert, the footlambert, and
the candela per unit of area. The lambert (L) is by definition the brightness of a perfectly
diffusing surface which radiates or reflects 1 lm/cm2, while the millilambert (mL) is 0.001
of this value. The footlambert (fL) is the brightness of a surface which radiates or reflects
1 lm/ft2. As its name implies, the candela per square inch is the brightness of a surface
which radiates 1 cd/in2. The lambert and the candela per square inch are commonly used
for high brightness such as light sources, while the millilambert and the footlambert are
used for designating ordinary illuminated surfaces.
41. The working equations for brightness computations are
b 2.05 L
(3)
F 6.45 SL
(4)
where b brightness in candelas per square inch, L brightness in lamberts, F total
luminous flux in lumens, and S area of the surface in square inches.
EXAMPLE
A light source has a brightness of 500 cd/in2. What is its brightness expressed
in lamberts?
SOLUTION
By transposing terms in Formula (3) above:
L
500
b
243.5 L
2.05
2.05
EXAMPLE An incandescent-lamp filament has a surface area of 0.4 in2 and emits 1580 lm.
What is its brightness in lamberts?
SOLUTION
By transposing terms in Formula (4) above:
L
1580
b
612 L
6.45S
6.45 0.4
42. The relation between the illumination incident on and the brightness
reflected from an illuminated surface can be understood from a consideration of
the following facts. No surface, however smooth, is a perfect reflector, since some of the
luminous flux impinging on the surface will be absorbed thereby. Therefore, when the surface brightness resulting from the reflection of the impinging light rays or illumination is
computed, the coefficient of reflection (Table 9) of the material must be considered. The
brightness equals the illumination times the coefficient of reflection.
mL 1.076 E m mL
(5)
where mL average surface brightness over the surface under consideration in millilamberts; E the incident illumination on the surface in footcandles; and m the absolute
coefficient of reflection (Table 9) of the surface material.
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ELECTRIC LIGHTING
10.22
DIVISION TEN
EXAMPLE
SOLUTION
A surface of white plaster has illumination of 5 fc. What is its brightness?
The coefficient of reflection of white plaster (Table 9) is 0.90. By Formula (5),
Brightness 1.076 E m 1.076 5 0.90 4.84 mL
43. Conversion Factors for Various Units of Brightness
Values in units in this column conversion factor values in units
at top of column
Candelas/in2
Lamberts
Millilamberts
Footlamberts
Candelas/in2
Lamberts
Millilambert
Footlambert
1
2.054
0.00205
0.00221
0.487
1
0.001
0.00108
487
1000
1
1.076
452
929
0.929
1
44. The maximum brightness beyond which glare will result (see Sec. 38) from a
lighting unit usually should not exceed from 1 to 1.56 (2 to 3 cd/in2 of projected area) in the
central portion of the visual field. Higher values of brightness will produce a sensation of
glare. The value depends on the size of the source, the position in the line of vision, and the
contrast between the source and its surrounding. If the eyes are not to be fatigued when the
unit is viewed continually, the brightness should not exceed 0.25 L. It should be noted
that the maximum permissible brightness is somewhat influenced by the darkness of the
surroundings (see Sec. 38).
44A. Brightness of Light Sources
Source
Incandescent lamp with opal globe
Incandescent lamp, inside-frosted globe
Fluorescent lamp, white and daylight
Fluorescent lamp, green
Fluorescent lamp, red
Fluorescent lamp, pink, blue, or gold
Candle flame
Acetylene-burner flame
Vacuum-incandescent-lamp filament
Gas-filled-incandescent-lamp filament
Neon tube, red
Neon-mercury tube, green or blue
Mercury arc (quartz tube)
Metal halide arc
High-pressure sodium arc
Sky
Sun, on horizon
Sun, 30 above horizon
Sun, at noon
Ceiling over indirect-lighting fixture
Walls when lighted by diffused daylight
Approximate lamberts
0.24–1.46
7–15
1.2–2.6
2.4–3.6
0.12–0.23
0.83–1.8
1.46–1.95
29–50
460–700
3,000–4,000
0.24
0.05–0.1
290–490
1,100–1,700
1,100–1,900
0.7–2.0
1,000
243,000
450,000
0.01–0.1
0.001–0.05
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.23
45. Brightness (or luminance) is usually measured by portable meters which operate on the same
basic principle as the footcandle meter. Brightness
meters use a photoreceptor such as a photomultiplier
tube or photovoltaic cell which creates an electrical
signal in proportion to the brightness of an object or
surface. Some form of optical system is designed into
the meter to permit the operator to focus on the meter
or the object or surface being measured. The electrical
signal is sent through an amplification circuit to the
meter, which may be either analog or digital. With
proper calibration, a direct reading of brightness is
obtained. A typical portable brightness meter is shown
in Fig. 10.22.
46. Fiber optics is a relatively new optical tech- FIGURE 10.22 Portable brightness
nology that refers to optical systems consisting of thin meter. [Minolta Corporation]
cylindrical glass or plastic fibers with excellent optical
properties. Light enters one end of a fiber and is transmitted along the fiber core to the other
end by internal reflections off the clad or fiber wall (Fig. 10.23). Large quantities of fibers
are placed together to form a bundle. Each fiber is insulated with a special glass coating to
prevent light from transforming one fiber to another. The bundle has external tubing to protect the fibers, and the ends of the bundle are bonded and polished. Initial use of fiber optics
was in medical applications to observe conditions inside the human body. The most significant application has been in optical communications where voice signals are encoded and
transmitted at high speed over the fibers. Fiberoptic systems have two advantages over conventional cable transmission systems: they are free
from cross talk, and they are unaffected by random
electrical disturbances such as lightning. Refer to FIGURE 10.23 Light transmission
through optical fibers.
Div. 11 for detailed coverage of this topic.
In lighting applications, fiber optics are being used in some automobile models to monitor information on signal-light operation on the dashboard as well as in optical sensors in
varying applications. They have also been used in signs and other advertising and decorative applications to create unique effects of colors and/or motion.
ELECTRIC-LIGHT SOURCES
47. Electric-light sources may be classified as follows:
A. Visible-light sources
1. Incandescent (filament)
2. Fluorescent
3. High-intensity–discharge (mercury, metal halide, and high-pressure sodium)
4. Other gaseous-discharge
a. Low-pressure sodium
b. Neon
c. Glow (argon and neon)
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ELECTRIC LIGHTING
10.24
DIVISION TEN
B. Ultraviolet-light sources
1. Sunlight lamps
2. Black-light lamps
3. Germ-killing lamps
4. Photochemical lamps
C. Infrared heating lamps
INCANDESCENT (FILAMENT) LAMPS
48. The incandescent lamp consists of a filament which is a highly refractory conductor mounted in a transparent or translucent glass bulb and provided with a suitable electrically connecting base. The filament is heated by the passage of an electric current through
it to such a high temperature that it becomes incandescent and emits light. In incandescent
lamps of the older types the air was, insofar as practicable, exhausted from the space within
the bulb and surrounding the conductor (filament), forming a partial vacuum. But in many
of the modern lamps this space is filled with an inert transparent gas such as nitrogen. The
conductor must have a high melting point or a high vaporizing temperature and a high resistance; it must be hard and not become plastic when heated. In vacuum-type lamps the vacuum must be good, not only to prevent the oxidation of the filament but also to prevent the
loss of heat, which would reduce the efficiency. In non-vacuum-type lamps (gas-filled
lamps) the gas used must be inert so as not to combine chemically with the filament material.
The bulb must be transparent or translucent to permit the passage of light, not porous, so that
it will retain the vacuum or inert gas, and strong to withstand handling and use.
49. Classification of incandescent lamps. Incandescent lamps may be classified
in six different ways, according to:
1.
2.
3.
4.
5.
6.
The class of lamp
The shape of the bulb
The finish of the bulb
The type of the base
The type of filament
The type of service
50. Class of lamp. Incandescent lamps are classified as Type B or Type C. The Type
B lamp is one in which the filament operates in a vacuum. The type C lamp is one which is
gas-filled. Gas-filled lamps are the most widely used types. The gas reduces the rate of sublimation of the heated filament. Inert gases such as nitrogen, argon, and krypton are in common use today, with krypton used where its increased cost is justified by increased efficacy
or increased lamp life. For example, the 90-W krypton “energy-saving” lamp produces 4%
less light, but one-third longer rated life compared with the standard 100-W lamp.
51. Classification according to shape of bulb (Fig. 10.24). The standard-line
shape is employed for general-lighting-service lamps up to and including the 100-W size.
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ELECTRIC LIGHTING
10.25
FIGURE 10.24 Typical bulb shapes and designations (not to scale). Most high-intensity discharge
(HID) lamps are BT-, E-, ED-, PAR-, and R-shape bulbs.
Lamps of 150 W and larger for general lighting service are made in the pear shape. The
other shapes are utilized for lamps designed for special classes of service. Lumiline lamps
are included in the tubular classification.
Shape of bulb
Designating letter
Standard-line
Bulb-tubular
Cone-shaped
Flame-shaped
Globular
Parabolic
Pear-shaped
Reflector
Straight-side
Tubular
A
BT
C
F
G
PAR
P or PS
R
S
T
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ELECTRIC LIGHTING
10.26
DIVISION TEN
Lamps are designated by a letter and figure such as PS-30. The letter indicates the shape
of bulb and the figure the greatest diameter of the bulb in eighths of an inch. Thus, a PS-30
lamp is a lamp with a pear-shaped bulb with a diameter of 30/8, or 33/4 in.
52. Classification according to finish of bulb
1.
2.
3.
4.
5.
6.
7.
8.
9.
Clear
Inside-frosted
Silvered-bowl
White
Daylight
Inside-colored
Outside-colored
Colored-glass
Outside-coating
53. Finish of bulbs. Incandescent lamps can be
obtained with the bulbs finished in several different ways as
listed in Sec. 52. With the clear lamps the bulb is made of
clear glass which leaves the filament exposed to view.
Clear-bulb lamps are used with reflecting equipment which
completely conceals the lamp from view. They are
employed with open-bottom types of reflecting equipment
in some cases when the units are mounted so high that the
lamps are not in the line of vision. Inside-frosted lamps have
the entire inside surface of the bulb coated with a frosting
which leaves the exterior surface perfectly smooth. This finish
conceals the bright filament and diffuses the light emitted
from the lamp. Inside-frosted lamps are used with openbottom types of reflecting equipment and in places where no
reflecting equipment is employed. Silvered-bowl lamps
(Fig. 10.25) have a coating of mirror silver on the lower half
of the bowl, which shields the brilliant filament and forms a
highly efficient reflecting surface for indirect lighting. The
upper part of the bulb is inside-frosted to eliminate streaks
and shadows of fixture supports. Silvered-bowl lamps
FIGURE 10.25 Silvered-bowl
should be used only in fixtures designed for them, because
incandescent lamp.
the silvering directs the heat toward the socket assembly,
which will therefore tend to operate at a higher temperature
than with clear lamps. White lamps have the entire interior surface of the lamp covered
with a fine coating of silica. This coating gives a high degree of diffusion which softens
shadows and reduces shiny reflections. Since bulb blackening is not apparent through the
diffusing coating, the lamps appear clean and white throughout their life.
54. Daylight lamps have a blue bulb made of a special blue-green glass to approximate noon sunlight. The ordinary incandescent lamp produces light in which the red rays
predominate. The blue-green glass of the bulb of daylight lamps absorbs part of the reddish
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.27
rays emitted by the filament of the lamp, giving a light which approaches the whiteness of
noon sunlight. The glass absorbs about one-third of the total light emitted by the filament.
55. Colored bulbs. Colored light is obtained from filament lamps by the subtractive
method, that is, by means of a separate filter or a bulb so processed that light of colors other
than that desired is largely absorbed. Colored bulbs used in lamp manufacture are of
natural-colored glass or of clear glass having a coating applied to either the inner or the
outer surface of the bulb by one of several different processes. Natural-colored bulbs,
wherein chemicals are added to the ingredients of the glass to produce the desired color, are
regularly available in daylight blue, blue, amber, green, and ruby. Natural-colored bulbs
produce light of purer colors than coated bulbs and are often used in preference to the
latter for theatrical and photographic lighting.
Coated colored lamps are made by spraying either the inside or the outside of the bulb
or by applying a fused enamel (ceramic) or acrylic coating to the outside of the bulb. The
colors in most common use are red, blue, green, yellow, orange, and white.
When decorative or display lighting is involved, coated colored lamps are to be preferred to natural-colored lamps because of their lower cost. Enameled, acrylic-coated, and
inside-sprayed bulbs are satisfactory for either indoor or outdoor use.
56. Tungsten-halogen lamps are incandescent (filament) lamps but are significantly different from conventional lamps in size and design. They represent the practical
application of the halogen regenerative cycle in filament lamps. All tungsten-halogen lamps
are filled with a gas of the halogen family. Iodine and bromine are the most commonly used.
As the lamp burns, the halogen gas combines with the tungsten that is sublimated from the
filament. As the gas circulates inside the bulb, the tungsten is deposited back on the filament
rather than on the inside bulb wall. This keeps the bulb wall clean and allows the lamp to
deliver essentially its initial light output throughout life. Owing to the lamp temperatures,
quartz or a special high-silica “glass” are used for the lamp bulb or filament tube.
Four types of tungsten-halogen lamps are available (Fig. 10.26). The most widely used
designs are the small tubular double-ended lamps. A coiled filament extends from one end
of the lamp to the other. Lamp wattages range from 200 to 1500 W. A second type utilizes
FIGURE 10.26 Tungsten-halogen lamps. The PAR design is cut
away to show the internal filament tube.
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ELECTRIC LIGHTING
10.28
DIVISION TEN
a base at only one end of the quartz bulb. In the third type, the quartz filament tubes are
sealed into outer bulbs such as PAR lamps for good optical control.
The last type of tungsten-halogen lamp for lighting is an adaptation of the small photographic halogen projection lamp. Small 12-V quartz filament tubes are mounted in small
multifaceted glass ellipsoidal reflectors with infrared transmitting reflectors which reflect
light but transmit much of the infrared heat out the back of the lamp. These lamps are extensively used in display-lighting applications.
The average life of most general-lighting tungsten-halogen lamps is about twice the life
of regular general-service incandescent lamps, or 2000 h. Although for the same wattage
the initial light output of these lamps is about the same, at the end of 1000 h the tungstenhalogen lamp produces about 13 percent more light than the standard general-service lamp.
These lamps offer high light output from compact lighting equipment. For example, the
reflector for the 1500-W T-3 tungsten-halogen lamp is only 1 ft (0.3 m) long and 6 to 7 in
(152 to 177 mm) wide.
Tungsten-halogen PAR lamps combine the excellent efficiency and long life of quartz
lamps with the light control of a PAR bulb. The quartz tube is mounted at the focal point of
the PAR bulb’s reflector for accurate beam control. At the end of life (4000 h), 500-W
tungsten-halogen PAR lamps provide 40 percent more light than standard 500-W PAR lamps
rated at 2000 h. Special infrared reflecting films are utilized on the inner surface of the bulb
or filament tube of some halogen lamp designs. This film transmits visible light but reflects
infrared energy back to the filament, thus reducing the input power required to achieve the
desired filament temperature and increasing lamp efficiency by as much as 50 percent.
Tungsten-halogen lamps are widely used in general lighting and floodlighting. Special
tungsten-halogen designs are also used in specialty applications such as stage, film, and TV
lighting, copying machines, and optical devices.
56A. Classification According to Type of Base (Fig. 10.27)
Bayonet
Candelabra
Intermediate
Medium
Three-contact medium
Admedium
Mogul
Three-contact mogul
Disc
Medium prefocus
Mogul prefocus
Medium bipost
Mogul bipost
Medium skirted
Minicandelabra
Recessed single-contact
Mogul end-prong
Extended mogul end-prong
Medium two-pin
Medium side-prong
Candelabra prefocus
Screw terminal
Lug sleeve
Two-pin
Double-contact medium
57. Lamp bases. A number of different types of bases for incandescent lamps (Fig. 10.27)
are in use. Of these, the bayonet, candelabra, and intermediate base are used on small-size
(miniature) lamps. The medium base, used on general-service lamps of 300 W and less, is
the most common type. The mogul base is used on sizes of 300 W and up. The admedium is
slightly larger in diameter than the medium and is used on some mercury lamps. The threecontact base is used with a three-lite type of lamp. The disc base is used on Lumiline lamps.
The medium and mogul prefocused bases are used on certain types of concentratedfilament lamps, such as those for picture projection and aviation service, for which it is
desirable to have the light source accurately located. The medium bipin base is for fluorescent lamps. The medium bipost base is made in 500-, 750-, and 1000-W lamp sizes for use
principally with indirect fixtures, for which it allows a better design of fixture and better
radiation of heat than are obtainable with the mogul-base type. For the very large-size
lamps of 1500 W and up for floodlighting service the mogul bipost is the standard.
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ELECTRIC LIGHTING
FIGURE 10.27
10.29
Bases for incandescent lamps. [General Electric Co.]
58. Classification according to type of filament. Several different types of filament structures are used. The filament structure is designated by a letter or letters to indicate whether the wire is straight or coiled and by an arbitrary number sometimes followed
by a letter to indicate the arrangement of the filament on the supports. Prefix letters include
S (straight; wire is straight or slightly corrugated), C (coil; wire is wound into a helical coil,
or it may be deeply fluted), and CC (coiled coils; wire is wound into a helical coil, and this
coiled wire is again wound into a helical coil).
59. Classification of incandescent lamps according to type of service:
1. General lighting service
a. Clear bulb
b. Inside-frosted bulb
c. Silvered-bowl bulb
d. White bulb
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ELECTRIC LIGHTING
10.30
DIVISION TEN
2. Special lighting service
a. Daylight lamps
b. Decorative lamps
c. Rough-service lamps
d. Three-lite lamps
e. Tubular lamps
f. Vibration lamps
3. Miscellaneous lighting service
a. Appliance- and indicator-service lamps
b. Aviation-service lamps
c. High-voltage lamps
d. Low-voltage lamps
e. Marine-service lamps
f. Mine-service lamps
g. Optical-service lamps
h. Photographic lamps
i. Photoservice lamps
j. Projection lamps
k. Projector and reflector lamps
l. Sign lamps
m. Spotlight- and floodlight-service lamps
n. Street-lighting–service lamps
o. Traffic-signal lamps
p. Train- and locomotive-service lamps
60. General-lighting-service lamps are those of 120- or 130-V rating for ordinary
uses in homes, stores, offices, schools, factories, etc.
61. Special-lighting-service lamps are for use in similar locations, but they have a
special design feature, such as shape or color of bulb, or other special features.
For an explanation of daylight lamps refer to Sec. 54.
Decorative lamps for general and special lighting are colored lamps that are available in
a number of different types (see Sec. 55). They can be used to provide special effects in
homes, theaters, shops, restaurants, and lobbies and foyers of public buildings.
Special yellow enameled lamps, which often are called “bug” lamps, are available.
Although these lamps are excellent for decorative lighting, they are designed primarily for
outdoor lighting during the season of night-flying insects. They have less attraction for
insects than lamps of other colors. These lamps are used in open porches, outdoor recreation areas, filling stations, camps, roadside stands, and any other place where people enjoy
outside activities under lights.
Rough-service lamps are specially constructed so that the filament can withstand sudden bumps and other forms of rough treatment. They are used principally in extension-cord
service in garages, industrial plants, and similar applications in which they will be subjected to excessive shock in service.
For an explanation of three-light lamps refer to Sec. 62.
Tubular incandescent lamps for special general-lighting service are available in the
Lumiline type and the showcase type.
The Lumiline lamps with their long bulb, 1 in (25.4 mm) in diameter, give a continuous
line of light which is well suited to places where space is limited, as in displays, niches,
small coves, signs, mirrors, paintings, and luminous panels. These lamps have contact caps
of the disk-base type at each end of the bulb. Specially designed sockets or lampholders are
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.31
required. Lumiline lamps are available with clear, inside-frosted, white, or colored-glass
tubes.
Showcase lamps (Fig. 10.28) are tubular lamps with conventional screw bases, which
are designed primarily for the lighting of showcases but which also are used for the lighting of shallow-depth displays and other special applications requiring small trough-type
reflectors. These lamps are available in clear, inside-frosted, and special showcase-reflector
types. The showcase-reflector type is made with a tubular bulb with the upper half insidealuminized so that it can be used in showcases, shelves, speakers’ stands, and the like, in
an ordinary socket without any reflector. A spring contact on the base allows the lamp to
be adjusted in the socket to throw the light rays in any desired direction.
FIGURE 10.28
Showcase lamps. [General Electric Co.]
Vibration lamps are designed particularly for use on or near rotating machinery and other
places where relatively high-frequency vibration exists. Certain of these lamps are equipped
with a special type of filament wire designed to operate suitably under vibration conditions.
62. The three-light lamp has two separate
filaments in one bulb (Fig. 10.29). One filament
consumes twice the wattage of the other, and the
filaments can be lighted separately or together to
produce three different levels of illumination, such
as 50/100/150 W or 100/200/300 W. These lamps
are particularly applicable to study lamps, reading
lamps, and indirect floor lamps so that the user,
with a single lamp, can adjust the illumination
from that for decorative and casual use to full brilliancy for close seeing. They can also be used in
stores so that daylight can be supplemented with
an economical use of electric light and the illumination can be varied to suit different occasions.
63. Appliance- and indicator-service lamps
are specially designed for use with appliances and
equipment for home and commercial use. These
lamps, when properly used, provide effective illumination of equipment exteriors and interiors and also
give clear indications of operations in progress.
FIGURE 10.29
Electric Co.]
Three-lite lamp. [General
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ELECTRIC LIGHTING
10.32
DIVISION TEN
64. Aviation-service (airport) lamps are designed to suite the special conditions encountered in the vital lighting for safety at airport landing fields. Several types
are required to provide satisfactory approach, beacon, running, taxiway, and the like,
lighting.
65. High-voltage–service lamps, rated at 230 and 250 V, are available for use in
locations where only the higher voltage is available. These lamps are less rugged and less
efficient than the general-lighting-service type. The reason for this is that the filament must
be of longer and finer wire to have sufficient resistance to limit the current to approximately
one-half the value for the same-wattage general-service lamp. For this reason use in any
new installation in which the lower voltage could be made available is not encouraged.
There are also general-service incandescent lamps of 277-V circuits. One manufacturer
cautions that such lamps be enclosed if used on high-capacity, low-impedance electrical
distribution systems.
66. Low-voltage–service lamps, rated at 6, 12, 30, 32, 60, and 64 V, respectively,
are available for use on electrical systems such as those of automobiles, boats, garden lighting, miniature interior fixtures or desk lamps, underwater swimming-pool fixtures, batterygenerator sets, and trains.In contradistinction to the high-voltage lamps, the filaments are
much thicker, providing inherent resistance to vibration and shock. The practical lower
limit of lamp voltages is about 1.5 V, because below that point the current required to heat
the filament begins to excessively heat the support wires.
67. Marine lamps are specially designed to take care of the special maritime illumination requirements. These lamps are used on shipboard to outline and identify vessels for
seaway safety and to signal between ships. On land, they provide a source for lighthouse
beacons. Underwater, they illuminate areas where divers must work.
68. Mine lamps are specially designed to meet the conditions encountered in the general illumination of mines and mine equipment.
69. Lamps for optical devices are available in a great variety of types to meet
the special requirements of devices used in the optical field of science, industry, and
education.
70. Photographic lamps are spotlight lamps designed with concentrated filaments
for maximum light output in the controlled beams of spotlights used in theaters, television
studios, and motion-picture and other photographic studies. For best lighting results, the filaments of these lamps must be accurately positioned, and the lamps should include mounting characteristics that will properly locate the filament in relation to the spotlight optical
system. These lamps operate at a higher color temperature and have a shorter life than
lamps for general service.
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ELECTRIC LIGHTING
10.33
71. Photoservice lamps are made in two types:
1. Photoflash lamps
2. Photoflood lamps
The photoflash lamp is used to illuminate scenes for the taking of photographs. The
photoflash lamp (Fig. 10.30) consists of a bulb containing flammable material such as zirconium in an atmosphere of oxygen. When the lamp is connected to a source of voltage,
the foil burns with a single brilliant flash lasting about 1/50 s. Photoflash lamps are generally used with older cameras. Most cameras today utilize small electronically ignited xenon
flash tubes which can be flashed repeatedly.
FIGURE 10.30
Photoflash lamps. [General Electric Co.]
The photoflood lamp is used for continuous illumination in the taking of moving pictures, by commercial photographers for studio portrait work and by amateur photographers for interior photographs. The photoflood lamp is similar to the regular insidefrosted incandescent lamp except that the filament is designed to operate at a higher
temperature. This lamp emits much more light than the general-service lamp for the
same wattage, but its life is much shorter, for example, 2 h for the smallest size to 10 h
for the largest size.
72. Projection lamps (Fig. 10.31) are used in slide and motion-picture projections. The lamps utilize carefully positioned concentrated filaments and a base type permitting accurate positioning of the filaments in the projectors. The filaments operate at
high temperatures, resulting in higher efficiency and thus shorter life, usually from 25
to 50 h.
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ELECTRIC LIGHTING
10.34
DIVISION TEN
FIGURE 10.31
Projection lamps. [General Electric Co.]
73. Reflector and projector lamps (Fig. 10.32) are made with a parabolic-shaped
bulb having a mirrored surface on the inside of the neck and a fixed-focus filament. They
can be used with a plain socket to form a highly efficient spotlight. The projector type has
a lens built into the face of the lamp for better control in the light. This lamp is made of
heat-resisting glass so that it can be used either indoors or in locations exposed to the
weather. The reflector type has an inside-frosted glass bulb which is not weatherproof and
does not provide so accurate a control of the light but costs only about two-thirds as much
as the projector type. Both types can be obtained in either a concentrating-spotlight or a
wide-floodlight version. These bulbs are available with integral quartz-halogen lamps. The
Energy Policy Act of 1992 established minimum efficacy standards for medium-base,
40–205-W, general service reflector and projector (R and PAR) lamps. As a result, many
previously popular R and PAR lamps are no longer manufactured for sale in the United
States. They have been replaced with more efficient halogen and halogen infrared PAR
lamps and krypton filled R lamps.
FIGURE 10.32
Reflector and projector lamps. [General Electric Co.]
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ELECTRIC LIGHTING
10.35
(Standard Handbook for Electrical Engineers) A number of projector lamps are available with dichroic filters (interference films) to control the spectral quality of the radiation
in such a manner as to separate the heat from the light in the beam or to produce colored
light without the usual losses due to absorption by filters. From 75% to 80% of the heat can
be removed from the beam at a sacrifice of only 15% to 20% of the light. These “cool
beam” lamps must be used in luminaires that are capable of dissipating the additional heat
that remains within the luminaire. Colored dichroic lamps produce more deeply saturated
colors with higher efficacy than is obtainable with color filters.
74. Sign and decorative lamps are lamps designed especially for outdoor
signs, Christmas and other decorations, carnivals, fairs, and festoon lighting. They are
used also for many interior applications. While many standard gas-filled lamps are
used in enclosed and other types of electric signs, those designated particularly as sign
lamps are mostly of the vacuum type. Lamps of this type are best adapted for exposed
sign and festoon service because the lower bulb temperature of vacuum lamps minimizes thermal cracks due to the contact of rain and snow. Some low-wattage sign
lamps, however, are gas-filled for use in flashing signs. This
causes more rapid cooling of the filament and reduces the
trailing effect which slow-cooling vacuum lamps might
produce. Bulb temperatures of these low-wattage gas-filled
lamps are sufficiently low to permit exposed outdoor use.
75. Spotlight and floodlight lamps have concentrated filaments, accurately positioned with respect to the base.
They are used in equipment which produces accurately controlled beams of light. There are several companion listings of
spotlight and floodlight lamps having the same dimensions but FIGURE 10.33 Floodlight
differing in life design. Floodlight lamps are used when burn- lamp. [General Electric Co.]
ing hours are long, as in building floodlighting and showwindow lighting. Spotlight lamps are used for applications in
which burning hours are short and higher light output is needed,
particularly in the blue and green portions of the visible spectrum. The T-12 and T-14 lamps are for use in ellipsoidal projectors when employed for show windows and interior
displays. The floodlight lamps are used also for underwater units.
A typical lamp is shown in Fig. 10.33.
76. Street-lighting–service lamps are lamps made
specifically for use in street-lighting luminaires. They are made
for series or multiple operation. A typical lamp is shown in
Fig. 10.34. The series lamps are for operation on constant-current
series circuits. They are made for 6.6- and 20-A circuits. Seriesconnected street lighting systems are rare today, but they are still
used for airport runway lighting.
FIGURE 10.34 Streetlighting–service
lamp.
[General Electric Co.]
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ELECTRIC LIGHTING
10.36
DIVISION TEN
77. Traffic-signal lamps (Fig. 10.35) are clear lamps
which are designed with a short light-center length for focusing the rays to give a signal indication of required brightness
for traffic-signal use.
78. Train and locomotive lamps are specially
designed to withstand the intense vibrations and shocks
encountered in this service. They are available in voltages
from 30 to 75 V for regular train-lighting service and for
locomotive-cab and headlighting service.
79. Burning position. With a few exceptions generallighting-service lamps can be burned in any position.
However,
the lumen maintenance of Type C lamps is best
FIGURE 10.35 Traffic-signal
when they are burned base up. This is because the tungsten
lamp. [General Electric Co.]
blackening is conducted upward by the gas and is always
deposited above the filament. When the lamp is burned base up, the blackening collects in
the area of the bulb adjacent to the base, where the light is already partially intercepted by
the base, socket, and luminaire husk. If the lamp is burned base down, the blackening collects in the bowl of the bulb, where it causes a much greater reduction in light output.
Lamps burned in a horizontal position are affected similarly.
Certain types of lamps, particularly projection, spotlight, floodlight, and some street
series lamps, are not designed for universal burning and should always be used in the position designated by the manufacturer’s published data. The reason for this may be the construction of the filament, which would be likely to sag or short-circuit if burned in a position
other than that for which it is designed. Operation in an incorrect position sometimes places
the filament directly under a glass part which might be softened by the heat. If a lamp containing a collector grid is burned in any other position than with the grid directly above the
filament, the special construction will not be effective in controlling blackening.
80. Lamp temperatures. Operation of lamps under conditions which cause excessive
bulb and base temperatures may result in melting of the bulb, softening of the base cement, and
loosening of the base or, in extreme cases, damage to the socket and adjacent wiring. Most fixtures are properly designed to dissipate the heat generated by the lamps, but severe conditions
such as might be induced by over-voltage operation or the use of lamps of higher wattage than
the manufacturer’s rating may give rise to difficulty. If metal parts of shades, reflectors, or fixtures are allowed to come in contact with the bulb of a gas-filled lamp, the local cooling effect
may result in glass cracks which will cause lamp failure (sometimes violent). Maximum safe
operating temperatures for best lamp performance are shown in the following table.
Maximum Safe Operating Temperatures
(Approximate figures)
Soft-glass bulb
Hard-glass bulb
Cemented base
Regular
Special Hi-Temp
Mechanical base
Bipost base
370C
450–510C
170C
200C
210C
285C
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10.37
Gas-filled lamps, because of the convection currents within the bulb, have higher bulb
temperatures than vacuum lamps. Therefore vacuum lamps are preferable for use in
exposed outdoor locations where snow or rain may strike the hot bulb. Gas-filled lamps
exposed to the elements should have hard or heat-resisting glass bulbs.
81. Vibration and shock. Tungsten wire heated to incandescence becomes somewhat soft and pliable, and filament coils may be distorted or broken if the lamp is subjected
to shock or vibration while burning. Vibration, especially of the low-amplitude highfrequency variety, is an insidious enemy of satisfactory lamp performance and should be
guarded against whenever possible. There are available a number of commercial sockets
and fixtures designed to protect the lamps by absorbing vibration.
If vibration cannot be eliminated by these means, special vibration-service lamps, provided with extra filament supports, should be used. The construction of vibration-service
lamps is such that they will give most satisfactory performance if burned in a vertical position, either base up or base down. They should never by used where they are likely to receive
extreme shocks.
For use on extension cords and in any service where excessive shocks may be encountered, there are available rough-service lamps with a special type of shock-resisting filament construction. Rough-service lamps are designed to operate in any burning position
and can be used in place of vibration-service lamps when it is necessary to burn lamps horizontally. Both vibration- and rough-service lamps sacrifice some efficiency to strength of
construction and are more expensive than standard lamps; they should, therefore, be used
only where required by service conditions.
82. The life of incandescent lamps is defined as the average life of a large group
of lamps burned under specified conditions. The range of typical mortality curves for
incandescent lamps is shown in Fig. 10.36.
FIGURE 10.36
Incandescent-lamp mortality curves. [General Electric Co.]
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ELECTRIC LIGHTING
10.38
DIVISION TEN
The average life of standard lamps for
general lighting purposes varies from 750 h
for some lamps and 1000 h for others to 2500 h
for certain sizes and types. Approximate
hours of life are specified by the manufacturer. The life of a lamp is materially affected
by the voltage impressed upon it. Operating
a lamp at less than its rated voltage will prolong the life of the lamp while operating at
higher than its rated voltage will shorten its
life. This does not mean that it is good practice to operate lamps at less than their rated
voltage. Decreasing the voltage on a lamp
decreases the light given out by the lamp, but
FIGURE 10.37 Variation in characteristics
the percentage of decrease in light is much
of incandescent lamps with voltage. [General
Electric Co.]
greater than the percentage of decrease in
voltage, so that the efficiency of operation is
much poorer. Figure 10.37 shows percentage variation in characteristics of lamps with variation from normal voltage. Consider a 120-V lamp operating at 114 V. The voltage
impressed on the lamp is 95 percent of rated voltage. From Fig. 10.37 the lumens emitted
by the lamp will be reduced to 84 percent of the rated value. Thus a 5 percent reduction in
voltage results in a 16 percent reduction in light output.
Lamp Package Labeling. The Energy Policy Act of 1992 mandated package labeling
requirements for most 120-V, medium-base, general service incandescent lamps under
200 W, 40–205-W, medium-base, general service incandescent reflector lamps, widely
used 2-U, 4 and 8 linear fluorescent lamps and integral-ballasted compact fluorescent
lamps. The requirements became effective during 1995.
Packages for general service incandescent and incandescent reflector lamps and
integral-ballasted compact fluorescent lamps must show light output, wattage, and life in
equal size on the package together with a statement on using the lowest wattage lamp with
the proper light output. In addition, general service incandescent reflector lamps must show
with an explanation that the lamp meets minimum federal efficiency standards. Specialty
incandescent and incandescent reflector lamps are exempt from the labeling requirements.
General service fluorescent lamps covered by the legislation must show a on the lamp or
enclosing sleeve. Similar information must also be included in manufacturers’ catalogues.
On point-of-sale materials, the assumptions in any comparisons must be stated. Current legislative activities related to energy policy have raised the bar again on incandescent lamps in
general, and over time this venerable light source may be relegated to specialty applications.
FLUORESCENT LAMPS
83. The fluorescent lamp (Standard Handbook for Electrical Engineers) is a lowpressure mercury electric-discharge lamp in which a phosphor coating transforms the ultraviolet energy generated by the discharge arc into light. The major parts of a fluorescent
lamp (hot-cathode type) are the bulb (tube), electrodes, fill gas, phosphor coating, and
bases, as shown in Fig. 10.38. When the proper voltage is applied across the ends of the
lamp, an arc is produced by current flowing between the electrodes through the fill gas
(mercury vapor mixed with argon or other inert gas). This discharge generates some visible
radiation, but mostly ultraviolet at 253.7 nm, which in turn excites the phosphor coating to
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FIGURE 10.38
10.39
Fluorescent-lamp construction. [General Electric Co.]
emit light. Fluorescent lamps are available commercially principally in four distinct types,
depending upon their operating circuits: (1) hot-cathode, preheat-starting; (2) hot-cathode,
instant-starting; (3) hot-cathode rapid-start; and (4) cold-cathode.
84. Fluorescent lamp bulbs (Standard Handbook for Electrical Engineers) are
basically tubular of small cross-sectional diameter. The bulb is available in straight, Ushaped, and circular configurations in bulb diameters from l/4 to 2 1/8 in. In straight
lengths, they range from 6 to 96 in (nominal). Shorter lamps, such as the 22-, 34-, and
46-in T-5 lamps, can simplify the design of luminaires for 600- and l200-mm module ceiling systems. Circular (Circline) lamps have nominal overall diameters from 61/2 to 16 in.
U-shaped lamps are 24 and 45 in. in nominal overall length. Fluorescent lamps are designated by a letter indicating the tube cross section shape and a number indicating the diameter in eighths of an inch. A T-8 lamp has a tubular bulb of 1 in. diameter. Smaller diameter
lamps and lower height ballasts can result in “thinner” luminaires. Generally speaking, the
thinner tubes offer increases in efficiency because the wall of the tube is closer to the internal arc path. They are also somewhat more temperamental because they want to run hotter
for this reason, and are more sensitive to cold air or drafts.
85. Compact Fluorescent Lamps. The newest types of fluorescent lamps are compact lamps ranging in wattage from 5 to 50 W (Fig. 10.39). Utilizing T-4 or T-5 tubing, the
basic lamp is formed in a biaxial or twin-tube shape with a single-end base. Other types
have been added which employ double, triple, or quad twin-tube designs resulting in a more
compact lamp design for a given lamp wattage.
The lower wattage twin-tube lamps are preheat designs with internal starters in the lamp
base. The higher lumen twin-tube lamps are a rapid-start design with 4-pin bases. The double and triple twin-tube types have both preheat designs with internal starters and two-pin
bases, and rapid start designs with 4-pin bases for external starters. Dimming systems are
available for rapid-start designs.
Double, triple, and quad twin-tube lamps with integral ballasts in the lamp base in addition to twin-tube and double twin-tube lamps utilizing plug-in adapters with built-in ballasts are available for replacement in medium-base incandescent fixtures where general
service incandescent lamps ranging in size from 25 to 100 W are installed. When replacing incandescent lamps with compact fluorescent lamps, care must be taken to ensure that
the optical and thermal characteristics of the fixture will result in satisfactory compact fluorescent lamp performance.
The newer corkscrew configurations offer improvements in lamp life and stability and,
like other fluorescent lamps, they save significant energy. An approximate rule of thumb is
to take the incandescent wattage and divide by four to get the replacement CFL wattage.
Fig. 10.40 shows a 14 W lamp, rated as equivalent to a 60 W lamp in output while increasing the relamping interval by a factor of eight. When a cold lamp is first turned on, the
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10.40
DIVISION TEN
FIGURE 10.39
Compact fluorescent lamps. [General Electric Co.]
brightness is about 80% of full, and full brightness is reached in about a minute. Different
color temperatures are available, allowing the owner to select a warmer or cooler white.
There are even multistage CFLs available to replace multiwattage incandescent lamps (e.g.,
50 W-100 W-150 W incandescent lamps in three-way sockets; see Fig. 10.62) widely used
in floor and table lamps. Be careful to read and observe any limitations placed on these
lamps by their manufacturer. Some are limited to dry locations; others need only be protected
from direct exposure to water; and most (but not all) must not be used with a dimmer.
Higher wattage compact fluorescent lamps provide the opportunity for efficient and
smaller fluorescent luminaires for general lighting applications. A new type of compact
FIGURE 10.40 A new, twisted-tube CFL. As can be seen to the left, this
one has a double-contact base, so it can operate at three different wattages.
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10.41
fluorescent lamp utilizes the glass tube formed in the shape of a square (similar to two D’s
back to back). Identified as a 2D lamp, they are available in several sizes from 10 to 38 W.
They provide the opportunity for shallow luminaire designs for ceiling or wall mounting.
The 101/2- and 221/2-in-long straight sizes are useful in 1- and 2-ft luminaires, and a threelamp, 2 by 2 ft recessed luminaire with 40-W twin-tube lamps can achieve so-called “nondirectional” layouts without significant reduction in total luminaire output compared with 2 4 ft units. Designers should check with lamp manufacturers about suitability for dimming.
86. Electrodes. (Standard Handbook for Electrical Engineers) There are two electrodes in each fluorescent lamp, one at each end, designed to operate as either “hot” or
“cold” electrodes (or cathodes). Figure 10.41 shows both types.
Hot-cathode lamps contain electrodes which are usually
coiled-coil (or triple-coiled) tungsten filaments coated with
one or more of the alkaline-earth oxides. By suitable circuit
arrangements these cathodes can be heated to an electronemitting temperature before the arc strikes, or they may be
required to act momentarily as cold cathodes until they are
heated by bombardment after the lamps have started. Lamps
using these cathodes may be designed to carry currents of 1 to
2 A with low voltage drop (10 to 12 V) at the electrodes. Some
energy-saving types of rapid-start ballasts have disconnect
elements to discontinue cathode heating after the lamp starts.
The power saved is approximately 3 W per lamp. Metal FIGURE 10.41 Cathodes
shields can be used to minimize end darkening, improving for fluorescent lamps.
lamp lumen maintenance.
Cold-cathode lamps are those that use electrodes of tubular form of iron or nickel which
may be coated on their inside surfaces with electron-emitting materials. These cathodes
operate at temperatures which limit the lamps to low-current densities. The electrode drop
in these lamps is relatively high (over 50 V), but they are not subject to short life as a result
of frequent instant starting.
87. Fill Gas. (Standard Handbook for Electrical Engineers) Droplets of liquid mercury are present in the fluorescent lamp and vaporize to a very low pressure during lamp
operation. Argon is added to assist ignition of the discharge in standard lamps, while
energy-saving types have an argon-krypton mixture. Certain other types use a combination
of argon and neon or argon, neon, and xenon.
88. Phosphors. (Standard Handbook for Electrical Engineers) The chemical composition of the phosphor coating on the bulb interior surface determines the color of the light
produced and, in part, lamp efficacy. Those lamps with phosphors producing good overall
color rendering are generally of higher efficacy.
The bulbs of some fluorescent lamps have a single, thick inner coat of conventional
“halophosphor.” Adding a thin coat of more expensive, rare-earth triphosphors can provide
an improved color rendering index (CRI) and increase the efficacy. When a double coat of
the triphosphors is used, CRIs are 80 to 90, while retaining the higher levels of lumens per
watt. Triphosphor coatings are standard on certain families of fluorescent lamps—check
manufacturers’ technical literature for current information, and for designations employed
with superior-color lamps. Special phosphors are also used in fluorescent lamps designed
for plant growth and for black-light effects.
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10.42
DIVISION TEN
89. Data on Fluorescent Phosphorsa
(In addition to the phosphor, manganese is usually present as an activator.)
Wavelength, nm
Phosphor
Barium silicate
Barium-strontium-magnesium
silicate
Cadmium borate
Calcium halophosphate
Calcium tungstate
Magnesium tungstate
Strontium halophosphate
Strontium ortho phosphate
Yttrium oxide
Zinc silicate
Exciting
range
Sensitivity
peak
Emitted
range
Emitted
peak
Black light
Black light
180–280
180–280
200–240
200–250
310–400
310–450
346
360
Pink
White
Blue
Blue-white
Greenish blue
Orange
Orange
Green
220–360
180–320
220–300
220–320
180–300
180–320
180–300
220–296
250
250
272
285
230
210
220–280
253.7
520–750
350–750
310–700
360–720
400–700
450–750
550–650
460–640
615
580
440
480
500
610
611
525
Lamp color
a
All values are given in nanometers. The nanometer, used to measure wavelength of visible radiation, is
1/1,000,000,000 m (1.0 10–9 m) in length.
90. Fluorescent-lamp colors. Fluorescent lamps are available in a range of strong
colors and in several different whites. The saturated colors—red, pink, gold, green, and
blue—are used for decorative effects, while the whites serve for both decorative and general lighting purposes. All fluorescent lamps except gold and red are white when unlighted.
Different phosphors produce the different colors when lamps are lighted.
White fluorescent lamps are designed to combine three elements important in lighting
effects: (1) efficacy (efficiency)—most light per dollar, (2) color-rendering properties—the
ability to bring out the beauty of colored materials and objects, and (3) whiteness—their
appearance in relation to either natural outdoor daylight or the traditional artificial illumination such as filament lamps.
The choice among fluorescent whites frequently involves compromise among these
three elements. Obtaining the best color-rendering properties can result in a reduction in
efficiency. Choice of whiteness may affect both efficiency and color-rendering properties.
The descriptions below outline the effects obtained from the most popular whites.
Cool white combines high efficiency with reasonably good color rendition. It is the
most widely used fluorescent-lamp color in factories, offices, and schools. It blends well
with natural daylight.
Warm white provides high efficiency with a warm tone. It emphasizes orange, yellow,
and yellow green at the expense of other colors. It is generally used where a warm tone is
more important than color rendition.
Deluxe cool white closely simulates the appearance and color-rendering properties of
natural daylight. It has been widely used in stores such as florist shops, menswear shops,
and other places where excellent color rendition of natural daylight is needed. It is also used
in factory and office applications in which best appearance of colors is important. It has
about 25 percent lower light output than cool white.
Deluxe warm white simulates the warm, effects of filament lighting in both whiteness
and color rendering. It has been used in residences, restaurants, beauty parlors, department
stores, bakeries, and other places where homelike lighting effects are wanted. For types
used in the home, deluxe warm white is also called soft white. Deluxe warm lamps provide
almost 30 percent less light than regular cool and warm white lamps. New rare earth phosphors have been developed which provide excellent color rendition in several warm and
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10.43
ELECTRIC LIGHTING
cool tones with no loss in light output compared with cool and warm lamps. The industry
designation for these colors is RE followed by a number which indicates color rendition and
color temperature. For example: RE730 has a color rendition index between 70 and 79 and
a color temperature of 3000 K; RE835 has a color rendition index between 80 and 89 and a
color temperature of 3500 K.
Special fluorescent-lamp colors have been developed for applications such as outdoor
plastic signs, color checking and matching in the textile and printing industries, the lighting of aquariums, and the growing of indoor plants.
Daylight, soft white, and white are still available for replacement purposes in existing
installations and for new installations in which their appearance or color-rendering properties are particularly suitable.
The Energy Policy Act of 1992 established minimum efficiency and color rendering
index standards for the widely used linear and U-shaped fluorescent types. As a result, cool
white, warm white, white, daylight, and deluxe warm white are no longer manufactured in
several of the previously available lamp types for sale in the United States. The rare earth
colors with comparable color temperature provide increased light output and efficiency
together with greatly improved color rendition. The older colors are still available as
replacements in the nonregulated lamp types.
91. Color Temperature and Color Rendering Index of Some Common Light
Sources* (Standard Handbook for Electrical Engineers)
Light source
Correlated color temperature, K
Color rendering index
“Cool” fluorescent
Standard cool white ES†
Cool white, ES, RE741 phosphor
Lite white, ES
RE841 phosphor
4150
4100
4200
4100
62
72
49
80
“Warm” fluorescent
Standard warm white, ES
Warm white, ES, RE730 phosphor
RE830 phosphor
RE827 phosphor
3000
3000
3000
2700
52
70
82
82
Deluxe daylight fluorescent, ES
RE950 phosphor
6500
5000
84
90
2600–3100
2900–3100
89–92
90
5710
4430
4000
3000
4200
2100
15
32
65
80–88
90
21
Incandescent
General service
Tungsten-halogen
High-intensity discharge
Mercury
Mercury improved color
Metal halide, clear
Metal halide, ceramic
Metal halide, ceramic
High-pressure sodium
Daylight
Overcast sky
Blue sky
Sun, outside of earth’s atmosphere
6000–7000
11,000–25,000
6500
*Check manufacturer’s technical literature for current data.
†
“ES” Energy-saving models
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10.44
DIVISION TEN
92. Bases. (Standard Handbook for Electrical Engineers) Lamps designed for instantstart operation generally have a base at each end with a single pin connection. (In some
cases instant-start lamps may have two pins at each end electrically connected.) Lamps for
preheat or rapid-start operation also have a base at each end, but with two pins (connections) in each. Some manufacturers use a green base finish or print to identify fluorescent
lamps which have less mercury and/or pass the toxicity characteristic leaching procedure
(TCLP), and therefore are classified as nonhazardous waste in many states. Rapid-start
high-output lamps have recessed double-contact bases, and T-2 subminiature fluorescent
lamps have axial bases. The Circline lamp has a single four-pin connector. Compact fluorescent lamps may have single two-pin or four-pin bases. Four-pin bases are required if the
lamps are to be dimmed. See Fig. 10.42 for images of the available fluorescent lamp base
types. Cold-cathode lamps are also instant-start lamps and have a single contact at each end,
usually in the form of a cap base.
93. Operation and starting of fluorescent-lamps. Fluorescent lamps are best
adapted to operate on ac circuits with reactance ballasts. The simplest operating circuit is
shown in Fig 10.43. When the luminaire is energized, current passes through the ballast,
creating magnetic flux, and also preheats the electrodes at each end which makes them
capable of thermionic emission. In the case of a luminaire with a starter, the starter
(Fig. 10.44) opens, which opens the flow of current through the ballast. Some luminaires
are simpler yet, and simply wait for someone holding their finger on the start button to
release it, causing the circuit to open in the same way. In either case the collapsing magnetic field in the ballast induces a relatively high voltage across the lamp, igniting it. Once
the arc is struck, the impedance of the lamp decreases to the point where, if connected
directly across the line, the resulting large current might destroy the lamp. However, the
ballast remains in series with the current passing through the lamp, the ballast reactance
opposes the flow of current, and the luminaire functions as intended.
Ballasts increase in complexity in instances where multiple lamps are being started and
where power factor must be corrected, but all fluorescent luminaires share a key performance attribute, namely: a fluorescent lamp has much lower impedance when lit than
when not lit. Therefore, all fluorescent luminaires have some method of striking the arc,
and controlling the passage of current after the arc has been struck.
Electronic ballasts (Sec. 106) take this to an entirely new level, because they are classified as either rapid-start, or instant-start, or programmed start. The latter designation is used
for ballasts that contain a microprocessor programmed to preheat the cathodes and increase
the starting voltage at an optimum temperature, shut off the cathodes when the arc is established, and to sense end-of-lamp life and disconnect the ballast until the lamp is replaced.
Electronic instant-start ballasts may give shorter lamp life due to harder starting that
puts more burden on the electrodes than do rapid-start and programmed-start ballasts, but
are lower in input wattage because there is no standby electrode heating. The savings in
kilowatt-hours often makes instant-start electronic ballasts the economic choice, unless
occupancy sensors (or other causes of frequent lamp cycling) turn the lighting off and on 7 or
more times each day. Users should also check with electronic ballast manufacturers about
level of line inrush current on starting.
94. General-line lamps. The 4-, 6-,8-, and 13-W T-5 fluorescent lamps are generally
used when space for lamps is limited and where the inherent cool light and color quality of
fluorescent lamps are desired. These are preheat lamps requiring a starter, and are rapidly
disappearing from new installations, but a great many are still in operation.
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10.45
FIGURE 10.42 Bases used for common types of fluorescent lamps: (a) regular fluorescent lamps, and (b)
compact fluorescent lamps.
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ELECTRIC LIGHTING
10.46
FIGURE 10.43
simple reactor.
DIVISION TEN
Circuit for fluorescent lamp and
FIGURE 10.44 Fluorescent-lamp starter switch
and socket. They are also available with an
internal normally closed switch that opens in the
event that the lamp will not restart after repeated
tries. If this occurs, a little button pops out on the
top of the starter, preventing a continuing annoyance and possible damage. The starter is easily
reset when the luminaire is relamped.
The 14-W T-8, 14-W T-12, 15-W T-8 and 15-W T-12 lamps are used in homes for
kitchens and mirror lighting. They are also used in stores for showcases, niches, and signs,
in industrial plants for local lighting at work stations, and in portable lamps.
The 20-W T-12 lamp was one of the most widely used fluorescent lamps. It was
employed in home fixtures for lighting in kitchens, bathrooms, basements, and recreation
rooms. It is used in window valances and under shelving and cupboards for decorative and
utilitarian lighting.
Several sizes of T-8 and T-12 lamps are available in lengths from 22 to 33 in (559 to
838 mm) for use in appliance and home applications. The 33-in 25-W T-12 is the longest
lamp which can be generated from 120 V ac with a simple reactor ballast.
The 25-W T-8 [36 in (914 mm) long] is used in stores for showcase, wall-case, and
perimeter lighting where its small diameter provides opportunity for good light control.
Modern T-8 lamps, often with electronic ballasts, are available in sizes that make most of
the preheat applications above obsolete.
The 32-W T-8 rapid-start lamp is used today in place of the former 40-W T-12 preheat
lamp and its successor, the 34-W T-12. The 40-W T-12 and the 40-W T-17 instant-start
lamp and 90-W T-17 preheat lamp are used only for replacement in older installations.
Newer fluorescent systems provide lower lighting costs in applications for these lamps.
95. High-output rapid-start lamps. The high-output line of T-12 lamps (24- to
96-in, or 610- to 2438-mm) operates at 800 to 1000 mA. Since the lamps are of rapid-start
design, two electrical contacts are required at each base. The recessed double-contact base
was developed to meet this requirement and, at the same time, to eliminate any hazard from
electrical shock.
A high-output rapid-start lamp gives about 40 percent more light than a conventional
lamp of comparable size. Because of the higher current load and thus higher bulb-wall
temperature, this lamp performs best in ventilated fixtures. Typical open-top fixtures that
allow substantial amounts of upward light provide excellent ventilation. Efficient surfacemounted and recessed fixtures have also been developed.
Because of the higher bulb-wall temperature, high-output lamps perform better in lowtemperature applications than 430-mA lamps. They are widely used in outdoor plastic-sign
applications.
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10.47
The highest-output fluorescent lamps
operate at 1500 mA. These lamps are available in T-10, T-12, and a noncircular PG-17
bulb (Fig. 10.45). The PG-17 is one of the
most efficient 1500-mA lamps for indoor
applications. This lamp has a U- or crescentshaped cross section. The exciting ultraviolet
radiation produced within the bulb has a
shorter distance to travel before striking the
fluorescent material or phosphor than it
would have from the center of a corresponding bulb of circular cross section. The full
benefit of the greater amount of ultraviolet
radiation generated is obtained with the Ushaped construction. Less opportunity is provided for reabsorption of this radiation by the
mercury vapor before it strikes the phosphor. FIGURE 10.45 1500-mA fluorescent lamps.
The rails along the grooves serve to keep the [General Electric Co.]
mercury pressure inside the bulb near the
optimum value by providing cool spots, which condense out excessive mercury vapor. The
bridges between the grooves assure adequate bulb strength.
The distribution of light from this lamp differs from that of conventional sources. The
total light in the 0 to 90 zone is equal to the total in the 90 to 180 zone, but in the 0 to 30
and 150 to 180 zones for the relative light output is approximately 12 percent more than
that from a tubular cross section of equal total light output. In most fixture designs this
directional effect can be used to advantage.
Like the high-output lamp, 1500-mA lamps maintain their light output well at low temperatures. Again, enclosed fixtures will provide maximum output in most low-temperature
applications.
For exposed lamp, outdoor applications, or indoor applications such as refrigerated
rooms for meat storage, jacketed T-10 and T-12 1500-mA lamps are available.
96. Slimline lamps are a family of fluorescent lamps which are instant-starting, with
single-pin bases. In general, they have advantages in wiring installation and maintenance
over other fluorescent lamps. The rugged single-pin base combined with push-pull insertion in sockets was very popular for some time, but their single-pin base reduces the design
options ballast manufacturers have to work with in terms of the latest energy saving possibilities. Slimline lamps are still available in a range of lengths and diameters to fit general
and supplementary lighting needs in most fields of application. These lamps have different
lengths than most of their bipin sisters, running almost 2 in. shorter. For example, a F48T12
slimline lamp is 46 in. long overall, instead of 47.78 in. for a comparable F32T8 or F34T12
bipin lamp. Do not make the assumption that you can rewire an existing slimline luminaire
to a conventional rapid start luminaire by simply changing the ballast and lampholders; the
luminaire will likely prove too short.
The 96T12 is the most prominent slimline lamp for general-lighting service. The maintenance advantages of the 8-ft (2.4-m) lamp result from fewer parts in the lighting systems
than preheat types require for the same amount of light—lamps, sockets, ballasts, starters,
and the like, being considered.
The 72T12 and 48T12 are 6- and 4-ft (1.8- and 1.2-m) companions, respectively, of the
96T12 which permit finishing out the ends of continuous rows in which the 8-ft lamp is
used. These lamps are also used for general lighting when shorter fixture lengths are desired
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ELECTRIC LIGHTING
10.48
DIVISION TEN
for scale or to fit an architectural module. The 24-, 36-, 42-, 60-, 64-, and 84-in (585-, 914-,
1067-, 1524-, 1626-, and 2134-mm) T-12 lamps are used primarily in outdoor plastic-sign
applications.
The 96T8 and 72T8 are available as replacements in existing installations. The smaller
diameter of these lamps makes them suited for use in coves or other restricted areas. New
96T8 lamps have been introduced with high efficiency, good color rendering rare earth
phosphors for use on electronic ballast systems.
The 42T6 and 64T6 are designed to fit standard 4- and 6-ft (1.2- and 1.8-m) store showcases. Their 3/4-in diameter means minimum visual obstruction for all types of displays. The
smaller diameter also permits accurate control with polished, concentrating reflectors for wallcase, show-window, cove, wall, or mural lighting and many other specialized applications.
97. Reduced-wattage fluorescent lamps in most of the widely used types and
sizes have been introduced to minimize energy consumption. Depending on the lamp type,
lamp wattage is reduced by 13 to 20 percent with minimal loss in light output. These lamps
use krypton in place of argon as the fill gas, which reduces the voltage across the lamps.
Reduced-wattage lamps are used on the same ballasts as standard lamps. They are available
for use in lighting fixtures intended for 30-W and 40-W rapid-start, 90-W T-17 preheat,
96-in (2438-mm) T-8 slimline, 48-in (1219-mm) and 96-in T-12 slimline, 48-in and 96-in
high-output, and 48-in and 96-in 1500-mA fluorescent lamps.
Reduced-wattage lamps are intended for use where lamp ambient temperatures are
60F (16C) or higher. Lamp flickering may occur where the lamp ambient temperature is
below 60F or where strong air drafts blow directly on bare bulbs.
The 40-W rapid-start lamps are available with an internal switch which removes the
cathode-heating current during lamp operation after the lamp has started to reduce energy
use further. Although these approaches are better than doing nothing, converting to modern T-8 or T-5 systems is preferable because of the inherent improvement in the lamp
geometry relative to the internal arc.
FIGURE 10.46 Circline fluorescent
lamp. Cases for fluorescent-lamp ballasts.
[General Electric Co.]
98. Circline lamps. Fluorescent lamps are also
made in the form of a circle. These are known as
Circline lamps. Circline fluorescent lamps (Fig. 10.46)
are now available in four diameters, 6, 8, 12, and
16 in. They are used in home lighting fixtures and
portable lamps. They are also used for decorative
lighting in restaurants, theaters, lobbies, lounges, and
other commercial areas. They are adapted for some
inspection processes in industry. The 6-, 8-, and 12-indiameter lamps have a preheat type of cathode and
can be operated on trigger-start ballasts. The 16-indiameter lamp is a rapid-start lamp.
Adapters or Circline lamps, including a ballast,
which permit their installation in incandescent
medium-base lampholders are available. They are
used in portable lamps as well as ceiling sockets for
incandescent lamps.
99. Ballast life and temperatures. The conventional ballast is enclosed in a container filled with a heavy impregnating compound which congeals around the choke coils
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10.49
and condenser. This serves to radiate heat and, by its compactness, to eliminate or minimize
noise or hum. Since the wattage loss in the ballast creates heat, suitable ventilation must be
provided in fixture design or in places where ballasts are installed to keep the temperature
within safe limits. If the temperature rises too high, the capacitor will fail and cause excessive heating and eventual failure of the internal windings.
Excessive ballast temperatures may be the result of one of the following:
1.
2.
3.
4.
Shorted starter in preheat circuits.
Burned-out lamp.
Rectifying lamp (near the end of lamp life).
Line-voltage fluctuation. Certain types of ballasts are sensitive to line-voltage fluctuation and therefore overheat at higher line voltages.
5. Improper design of fixture so that ballast heat cannot be dissipated efficiently.
6. Improper location of fixture which prevents proper heat dissipation.
7. Improper selection of ballast for the type of lamps used.
At a maximum temperature of 105C (221F) within the winding or 90C (194F) measured on the case and a maximum capacitor temperature of 70C (158F), the expected ballast life is about 12 to 15 years, depending on the operating hours each year. An increase of
10C (18F) beyond these limits will cut ballast life by as much as 50 percent.
The NEC requires that all fluorescent fixtures used indoors incorporate ballast protection other than that for simple reactor ballasts, as shown in Figs. 10.48 and 10.49. In
response to this Code rule Underwriters Laboratories has a standard that requires the use of
Class P (protected) ballasts for indoor fixtures. Class P ballasts contain inherent thermal
devices or thermal fuses, or both, which open automatically if the maximum temperature
of the ballast is exceeded. Only Class P ballasts should be used as replacements in fixtures
where ballasts other than reactor types are installed.
Although external fusing of a ballast (consisting of small quick-blow glass-tube fuses
rated close to the normal ballast current rating) provides some degree of ballast protection,
such fuses respond only to line current and not to temperatures inside the ballast. Since
some internal ballast faults will cause excessive temperatures without an increase in line
current, the fuse will not sense such faults. Accordingly, all present Class P ballasts contain
internal thermal devices or fuses which respond to internal temperatures. External fusing
will, however, provide a backup protection for Class P ballasts, and they will afford a high
degree of protection for other types of ballasts if sized according to the recommendations
of fuse and ballast manufacturers.
100. Radio interference. The performance of the mercury arc of a fluorescent lamp
at the electrodes is associated with an electrical instability that sets up a continuous series
of radio waves. There are three ways in which these waves may reach the radio and interfere with reception:
1. Direct radiation from the bulb to the radio aerial circuit
2. Direct radiation from the electric supply line to the aerial circuit
3. Line feedback from the lamp through the power line to the radio
The direct radiation from the bulb diminishes rapidly as the radio is separated from a
lamp, and this effect can be controlled by proper positioning of the radio and its aerial. The
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10.50
DIVISION TEN
following table shows the recommended distance of popular fluorescent lamps from an AM
radio antenna to minimize the effect of direct bulb radiation. This issue is much less of a
factor with FM radio, and may not arise at all depending on the listening habits of the occupants. In addition, the new electronic ballasts, operating in the 40–50 kHz range, don’t
impact media reception the way magnetic ballasts once did.
Recommended Distance from Lamp to AM Radio Antenna
Lamp size
14-, 15-, and 20-W
32-W Circline
30-W
40-W
90-W, 72- and 96-in slimline
Distance, ft
4
5
6
8
10
If the radio must remain within the bulb-radiation range, it will be necessary to take the
following precautions.
1. Connect the aerial to the radio by means of a shielded lead-in wire with the shield
grounded, or install a doublet type of aerial with twisted pair leads.
2. Provide a good ground for the radio.
3. The aerial proper must be out of bulb- and line-radiation range. The use of a correct
antenna system will usually help reduce radio interference by providing a better stationsignal strength.
The use of fixture-shielding material such as electrically conductive glass or special louver materials can aid in reducing radiated interference.
Interference from line radiation and line feedback can best be minimized by the proper
application of line filters at each lamp or fixture. A simple form of filter is a three-section
capacitor unit. One such unit per fixture, or for each 8 ft (2.4 m) of lamps in a cove, will
reduce line noise by approximately 75 percent. If it is desirable to eliminate line noise completely, the inductive-capacitor type is recommended. This filter has a current-carrying
capacity of 2 A, which is, for example, about the load of four 40-W lamps.
When only one or two radios are located near a fluorescent installation and the aerial
circuit has been properly shielded from bulb and line radiation, a single line filter located
at the radio power outlet will suffice.
When radios located in buildings adjoining the fluorescent installation are receiving
line-feedback type of interference, it is practical to install a single filter such as the threesection capacitor unit at each panel box feeding fluorescent-lamp circuits.
When it is necessary to filter each lamp or fixture, the filter should be located as close
to the lamps as possible. This precaution should be taken because of line radiation between
lamp and filter.
The improper spacing of lampholders, resulting in poor contact with lamp base pins,
can also generate interference, as can improperly grounded fluorescent fixtures. Failure to
ground the neutral of branch circuits (as required in the National Electrical Code) is an
additional cause. If the service lines are not properly grounded, filters will be much less
effective.
Fluorescent equipment destined for homes or other places where radios are likely to be
present should have the proper radio-interference filter in each fixture.
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10.51
101. The temperature of the bulb has a decided effect on the efficiency of a fluorescent lamp (Fig. 10.47). The best efficiency occurs at 100 to 120F (38 to 49C), which
is the operating temperature corresponding to an ambient room temperature of 70 to 80F
(21 to 27C). Efficiency decreases slowly as the temperature is increased above normal but
decreases very rapidly as the temperature is decreased below normal. For this reason the
fluorescent lamp is not satisfactory for locations where it will be subject to wide variations
in temperature. This reduction in efficiency with low surrounding air temperature can be
minimized by enclosing the lamp within a clear-glass tube or by using higher-current special fluorescent lamps designed for exposed low-temperature application (Sec. 95) so that
the lamp will operate at more nearly its desirable temperature (Fig. 10.48). Some CFLs
apply a mercury amalgam that provides more stable lumen output over a wider range of
temperatures and operating positions.
FIGURE 10.47 Effect of bulb-wall temperature
on the efficiency of the fluorescent lamp.
FIGURE 10.48 Effect of surrounding air temperature on the efficiency of the fluorescent lamp.
102. The life of a fluorescent lamp is affected not only by the voltage and current
supplied to it but also by the number of times it is started. Electron emission material is
sputtered off from the electrodes continuously during the operation of the lamp and in
larger quantities each time the lamp starts. Since life normally ends when the emission
material is completely consumed from one of the electrodes, the greater the number of
burning hours per start, the longer the life of the lamp. Depreciation of light output is caused
principally by tube blackening and is rapid (as much as 10%) during the first 100 h but very
gradual from that point on. For this reason lamps are rated commercially on the basis of the
lumen output after 100 h of operation. When the emission material is exhausted, lamps on
a preheat type of circuit will blink on and off as the electrodes heat but the arc fails to strike.
Lamps designed for instant or rapid start will simply fail to operate. Blinking lamps should
be removed from the circuit promptly to protect both the starter and the ballast from overheating.
The rated average life of a fluorescent lamp in burning hours is based upon the average
life of large representative groups of lamps measured in the laboratory under specified
test conditions. Many fluorescent lamps have a rated average life of 12,000 to 20,000 h
at 3 burning hours per start.
With the proper ballast operating voltage within the line-voltage limits shown on the
ballast label, rated lamp life should be obtained.
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10.52
DIVISION TEN
103. Power factor. (Standard Handbook for Electrical Engineers) A fluorescent
lamp, by itself, is inherently a high-power-factor circuit, but the reactive ballast normally
used to stabilize the arc is inherently low power factor. Since in the usual circuit the voltage
drop across the ballast is approximately equal to that across the lamp arc, the resulting power
factor of a single-lamp reactive-ballast circuit is on the order of 50%. For many applications
this low power factor is objectionable. In single-lamp ballasts, power factor correction may
be obtained by means of a capacitor shunted across the line connections or, where the lamp
requires a higher voltage, by a capacitor across the transformer secondary. The two-lamp
ballast, through phase displacement of the lamp currents, or series capacitors, offers a ready
means of power factor correction and is usually designed to give a circuit power factor
greater than 90%. Fig. 10.44 shows a representative example of this principle at work.
104. Variations in line voltage produce less effect on fluorescent lamps than on
incandescent lamps, the phase relationship among line voltage, lamp voltage, and auxiliary voltage being such that lamp voltage varies inversely as the square root of the line
voltage. For this reason, most fluorescent lamp ballasts are rated for a nominal circuit voltage of 120 V with an acceptable range of 110 to 125 V. Line voltage less than 110 may
make starting of the arc uncertain; a voltage over 125 may overheat the ballast. Line voltage less than 110 or greater than 125 can decrease the life of the lamp. Ballasts are also
available for widely employed lamp types for use on 277-V systems with an acceptable
range of 254 to 289 V. In addition, ballasts are available for some lamp types for 208-,
240-, and 480-V systems. Modern electronic ballasts are often available in configurations
that automatically detect and operate successfully on a full range of line voltages (see
Sec. 106) from 120 to 277 V.
Fluorescent lamps generally should be operated at voltages within 10% of their designed
operating points for best performance. Decreased life and uncertain starting may result from
operation at lower voltages, and at higher voltages there is danger of overheating of the ballast
as well as decreased lamp life. One exception to this is found in the series operation of coldcathode lamps where an adjustable voltage supply makes possible operation over a wide range
of illumination levels, that is, dimmer operation such as that used in stage lighting.
105. Noise ratings of ballasts. (Standard Handbook for Electrical Engineers) All
inductive fluorescent ballasts emit a certain amount of noise; the noise increases with the
lamp current. Ballasts are noise-rated according to laboratory standards. Such a rating is
only a guide for installation practice and does not attempt to specify one ballast type over
another for specific installations of fluorescent lamps.
Noise ratings are designated by letter, from A, the quietest, through F. The A rating is
best, for example, for home applications, in which the surrounding and competitive noise
level may be at a minimum. In an industrial plant with attendant operation noises, ballast
hum may be of no importance. Not all ballasts, regardless of their general noise rating, produce annoying hum or noise. Chances are that the noise potential of different ballast
designs is significant only in exceptionally quiet places. Individual ballasts of any noise rating may by some chance become offensive. Likewise, the ballast hum or noise vibration
may be induced into the wiring channel or fixture and may be minimized or emphasized by
the method used in mounting and clamping the ballast within the fixture. Electronic ballasts
are generally much quieter than magnetic ballasts and provide an “A” rating.
106. Electronic ballasts. While 60 Hz is the standard frequency for ac distribution,
higher frequencies have a number of advantages in the operation of fluorescent lamps. As the
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10.53
frequency increases, lamp efficacy is increased. The increase in efficacy depends on the lamp
type and the frequency of power delivered to the lamp. The gain in efficacy for 40-W T-12
rapid-start lamps is shown in Fig. 10.49. In addition, ballast losses are reduced, further
improving system efficiency, and ballasts can be smaller and lighter-weight since they do not
require the impregnating compound used in magnetic ballasts.
FIGURE 10.49 Effect of frequency on 40-W T-12
fluorescent-lamp efficacy. [General Electric Co.]
The use of solid-state electronic elements instead of magnetic components has made all
this a practical reality. (Standard Handbook for Electrical Engineers) It has made electronic ballasts the standard for today’s fluorescent lighting systems. Some use a control
chip that results in constant light output and energy consumption over a significant range
of line voltages. Electronic ballasts are lighter in weight, operate cooler, and can be
designed for rapid- and instant-start lamps to meet federal efficacy and FCC EMI/RFI standards. Some models permit dimming of fluorescent lamps, and can be used with appropriate sensors to compensate for changes in daylight illuminance levels. Electronic ballasts
cost more than electromagnetic types, but often provide swift payback for the lightinghours usage and kilowatt-hour rates typical of commercial, institutional, and industrial
applications. These ballasts operate on standard 60-Hz power systems but operate these
lamps at approximately 25,000–50,000 Hz.
These systems have far surpassed their predecessors. Earlier high-frequency systems
utilized central rotary or static inverters providing 360- to 400-Hz power with small capacitance- and inductance-type ballasts. These systems required separate electrical distribution
systems for lighting. High-frequency systems have been used on aircraft to reduce weight
with 400-Hz generators and small capacitive ballasts. In motor vehicles, lamps are operated
at variable frequencies up to 500 Hz.
Many electronic components are employed in assembling electronic ballasts. Their specific designs are considered proprietary, but Fig. 10.50 gives the block diagram for basic
electronic ballasts for fluorescent lamps.
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10.54
DIVISION TEN
FIGURE 10.50 Basic block diagram for electronic fluorescent lamp ballast (Courtesy of Osram/Sylvania Inc.).
Most ballasts for T-2, T-4, and T-5 fluorescent lamps sense deactivated-cathode “endof lamp life” conditions when one or more of the cathodes are depleted. This avoids a
potentially hazardous situation when those small-diameter lamps are used with electronic
ballasts, which could continue operating a bad-cathode lamp, perhaps causing the glass
at that end to melt or crack. Some electronic ballasts for T-8 rapid-start lamps are
expected to also incorporate end-of-life shutdown circuits.
107. Dimming. (Standard Handbook for Electrical Engineers) For dimming hotcathode fluorescent lamps, a number of different arrangements are available. For smooth
operation, the lamps on any circuit should be made by the same manufacturer, at the same
time, in the same color, and of the same age in use. Group replacement is the most satisfactory procedure. Lamps should be operated free from drafts at 50 to 80F and should
be seasoned 100 h at full brightness prior to dimming. Certain energy-saving lamps are
not recommended for dimming applications. Special dimming ballasts are typically
required.
Dimming ballasts are available to reduce light output of T-8 and T-12 rapid-start lamps
to 1%, 5%, or 10% of full lighting output. Most dimming ballasts are electronic ballasts.
Standard T5 lamps can only be dimmed to 5% while T5HO can be dimmed to 1%.
Compact fluorescent lamps can be dimmed to either 1% or 5%. Dimming ballasts offer
slightly lower lumens per watt than non-dimming electronic ballasts. One manufacturer
states that dimming from 100% to 1% and to 10% is perceived as 10% and 32% of full
brightness, respectively. Various sliding and other types of wall box and wireless dimmer
controls are available for dimming control, or in connection with occupant and daylight
sensors for automatic energy-conservation systems. Ballasts can be controlled via analog
or digital signals, and the controller must be configured to operate the type of ballasts being
used. Compatibility with emergency-lighting ballasts should also be explored.
108. Harmonic loading issues. (Standard Handbook for Electrical Engineers)
Due to the significant savings provided by electronic ballasts, most fluorescent ballasts
used today in commercial luminaires are electronic. The escalation of electronic dataprocessing equipment and variable-speed motors increased attention given to the harmonic content of electric power systems. Fluorescent-lamp ballasts are known to
contribute to total harmonic distortion (THD). Harmonics raise the current in the neutral
conductor of 3-phase, 4-wire, wye-connected power distribution systems, even though the
phase loads may be reasonably balanced. Some older circuits exist where reduced neutrals
are used for fluorescent lighting loads. However, full 100% capacity neutral conductors
have long been recommended for branch circuits consisting of more than one-half fluorescent
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10.55
lighting. Indeed, some electrical engineers specify cables with single, oversized neutral
conductors, cables providing a separate neutral for each phase, transformers designed to
handle harmonic loading, etc.
Both electronic and magnetic ballasts generate harmonics in the line current. For electronic types, most modern fluorescent ballasts limit the total harmonic distortion to under
20% or in some cases under 10%, neither of which should create problematic current in
the neutral conductor. Reported measurements of compact fluorescent lamps and diode
devices for use in incandescent-lamp sockets showed power factors in the 47% to 67%
range, and total harmonic distortion (THD) greater than 100%. Although electronic ballasts generally have lower THDs than do magnetic ballasts, check compliance with the
requirement of most electric utilities that the THD of electronic ballasts be less then 20%.
109. Where direct current is available (Standard Handbook for Electrical
Engineers) at circuit voltages comparable with the open-circuit voltages of the usual ac
ballast circuits, fluorescent lamps may be operated from these sources. For such operation,
resistance must be added to the usual series reactance ballast (transformer ballasts are not
applicable) to limit the operating current to the designed value. This causes a marked reduction in the overall efficacy of the lamp and circuit combination over that obtained in ac
operation. Under dc operation, lamps more than a few feet in length will promptly develop
a concentration of the mercury vapor at the negative end of the lamps, with the result that
only a fraction of the bulb will give off light. This condition can be overcome through a
periodic (about once in 4 h) reversal of the polarity of the lines feeding the lamps. The life
of lamps is likely to be shorter on dc.
110. Operating suggestions (General Electric Co.). To secure the best performance of fluorescent lamps, it is important that users understand how to maintain their fluorescent installations properly. Many factors that affect the performance of these lamps
were never encountered with incandescent filament lamps, and users must realize that some
of these elements of satisfactory service are within their control.
For example, if a filament lamp does not light when current is applied, the one single,
positive conclusion is that the lamp is burned out or defective. No such conclusion should
be made in the case of the fluorescent lamp. This lamp, though perfect in all respects, may
not start or operate properly through no fault of the design or manufacture of the lamp.
Average Life. Since mortality laws apply to fluorescent as well as to filament lamps,
it is not unusual for some fluorescent lamps to fail before rated life when life will last
for a longer period than their rated average life to balance out the normal early failures.
Normal Failure. The electroemissive material on fluorescent-lamp electrodes is used
up during the life of the lamp, the sputtering off being more rapid during starting.
Therefore, a longer life will be obtained if lamps are allowed to operate continuously
instead of being turned on and off frequently. Average rated life should be obtained if
lamps are operated for normal periods of 3 or 4 h with each start.
When the active material on the electrodes is used up, the lamp will no longer operate. On preheat circuits, it may continue to blink on and off as the starter attempts to start
the lamp. On instant-start circuits, the lamp may spiral at the end of normal life.
Swirling and spiraling. This phrase refers to all conditions in which the lighted lamp
appears to fluctuate in brightness from end to end. The cause is principally particles of
materials loosened from the cathode and floating in the arc stream. Such particles usually settle to the bulb when the current is turned off for a few minutes. This temporary
swirling may occur in new lamps and is not serious. If swirling persists, some operating
condition may be the cause of the particles being cast into the arc stream. High-impact
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10.56
DIVISION TEN
starting voltage may jar loose such material; this high-voltage starting may be due to
(1) a ballast of inadequate design, (2) a lack of proper starting aids in trigger-start and
rapid-start systems, (3) a starter in a preheat circuit that is not working properly to give
adequate preheat, or (4) any other circuit condition such as low supply voltage in which
neither starter nor ballast functions normally yet in which lamps may occasionally start
by high-voltage impact alone without preheat.
Instant-start lamps have cathodes designed to withstand high-voltage starting. When
new lamps of this type swirl persistently, the lamp may be at fault and should be
replaced. At the end of normal lamp life, when no electron-emissive material remains
on the cathode, the high starting voltage disintegrates even the metallic parts of the cathode, which then invade the arc stream. This is the cause of the excessive swirling that
characterizes the end-of-life period of instant-start lamps.
Normal Depreciation. The lighted output at 100 h is used for rating purposes because
the loss during this period may amount to as much as 10 percent. The average light output during life is approximately 90 percent of the 100-h rating value.
Blackening. A fluorescent lamp darkens rather uniformly throughout the length of the
tube during life, though this is not noticed unless an old lamp is compared with a new
one in front of a light source. At the end of life, the lamp usually shows a dense blackening either at one end or at both. Also, there may be dark rings, slightly brownish in
color, at one end or both. On the average, there should be little indication of either blackening or rings during the first 500 h of operation. If the lamp has not given a proper
length of service when this occurs, this may be due to improper starting, frequent starting with short operating periods, improper ballast equipment, unusually high or low
voltage, improper wiring, or a defect in the lamp.
End blackening should not be confused with a mercury deposit which sometimes
condenses around the bulb at the ends. This mercury condensation appears to be more
common with the 1-in- (25.4-mm-) diameter lamps than with the 11/2-in (38.1-mm) sizes. It
is occasionally visible on new lamps but should evaporate after the lamp has been in
operation for some time. However, it may reappear later when the lamp cools.
Frequently, dark streaks appear lengthwise of the tube as small globules of mercury cool
on the lower (cooler) part of the lamp. Mercury condensation is quite common on lamps
in louvered units owing to the cooling effects of air circulation around the louvers.
Mercury may condense at any place on the tube if a cold object is allowed to lie
against it for a short period. Such spots near the center section may not again evaporate.
When condensation occurs in this manner, rotating the lamp 180 in the lampholder may
give a more favorable position for evaporation or may place the spot in a less conspicuous place from an appearance standpoint.
Near the end of life, some lamps may develop a very dense spot about 1/2 in (12.7 mm)
wide and extending almost halfway around the bulb, centering about 1 in (25.4 mm)
from the base. This is quite normal, but a spot developing early in life is an indication
of excessive starting or operating current. This may be due to a ballast off-rating or to
an unusually high circuit voltage.
Occasionally a lamp may develop a ring or gray band at one end or at both. Such
rings are usually located about 2 in (50.8 mm) from either base. These rings have no
effect on the lamp performance and are no indication that a lamp is near failure and must
soon be replaced.
Circuit Voltage. The circuit voltage should be within the ballast rating, although 110to 125-V ballasts may in some cases give satisfactory lamp performance on circuits as
low as 105 V or as high as 130 V. Ballasts designed for 265 to 277 V may sometimes
give satisfactory results on line voltages as low as 260 V and as high as 285 V. Excessive
undervoltage or over voltage is injurious to the lamp.
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10.57
Ballast Hum. Characteristic transformer hum is inherent in lamp ballast equipment,
although the noise may come and go, varying considerably with individual ballasts. If
ballasts are mounted on soft rubber, neoprene, or similar nonrigid mountings, the vibrations due to the magnetic action in the chokes will not be transferred to supporting members, and disconcerting auxiliary hum will be reduced to a minimum. Such vibration
insulation, however, will inhibit heat radiation and transfer to such a point that ballast
ambient-temperature limits will be exceeded.
Low-Temperature Operation. In most cases, satisfactory starting and performance
can be expected at temperatures considerably below 50F (10C) by (1) keeping the
voltage in the upper half of the ballast rating, (2) conserving lamp heat by enclosure or
by other suitable means, and (3) using thermal starting switches.
Starting Difficulty. Starting difficulties may be due to a number of causes other than
the starter itself. In general, any difficulty in starting may result in premature end blackening and short lamp life.
A Lamp That Makes No Effort to Start. First the lamp should be checked to make
sure that it is properly seated in the sockets. If this fails to correct the trouble, the lamp
should be checked in another circuit, and, if necessary, the voltage can be checked at the
sockets. If no indication of power is found at the sockets, the circuit connections are
incorrect or the ballast is probably defective. In a preheat circuit, the starter should be
checked. It may have reached the end of life and should be replaced.
A Lamp That Is Slow in Starting. Low line voltage, low ballast rating, or in preheat
circuits a sluggish starter can also result in slow starting.
A Lamp the Ends of Which Remain Lighted. This condition indicates a short circuit
in the starter, which should be replaced. Starters that have been in service for some time
frequently fail in this manner. If the ends of a lamp in a new installation remain lighted,
it is possible that the wiring is incorrect. Of course, if short-circuiting types of No-Blink
or Watch-Dog (Fig. 10.44) starters are used, the lamp ends will remain lighted in a normally failed lamp; this condition automatically corrects itself when the failed lamp is
replaced with a new lamp.
A Lamp That Blinks On and Off in Preheat Circuits. Blinking is the usual indication
of a normal failure of a lamp. It will usually be found more convenient to put in a new
starter first and then, if blinking continues, to renew the lamp. Low circuit voltage, low
ballast rating, low temperature, and cold drafts may individually cause difficulties of
this nature, or several of these may be contributing factors. It is also possible for
improper circuit connections to cause such blinking. The annoyance of blinking lamps
can be avoided by using No-Blink starters in installations employing lamps for which
such special types of starters are available.
If the ends of a lamp remain lighted or the lamp blinks on and off, either the trouble
should immediately be corrected or the lamp or starter should be removed from the circuit. A blinking lamp can shortly ruin both lamp and starter. Ordinary starters can be
replaced with No-Blink starters (where these starters are available), which remove the
starter element from the circuit if lamps fail to light after a reasonable number of
attempts have been made.
Early End Blackening. Heavy end blackening early in life indicates that the active
material on the electrodes is being sputtered off too rapidly. It may be due to
1. High or low voltage. For best results, the circuit voltage should be within ballast
rating.
2. Loose contacts (most likely at the lampholder). Remedy: lampholders should be
rigidly mounted and properly spaced. See that lamps are securely seated in lampholders.
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ELECTRIC LIGHTING
10.58
DIVISION TEN
3. Improperly designed ballasts or ballasts outside specification limits. Remedy: the
use of ballasts approved by the Electrical Testing Laboratories will usually eliminate
trouble of this nature.
4. In preheat circuits a defective or worn-out starter, causing the lamp to blink on and
off, prolonged flashing of the lamp at each start, or the ends of the lamps remaining
lighted over a period of time. Remedy: replace with a new starter.
5. Improper wiring of units.
111. Induction fluorescent luminaires. (Adapted from Practical Electrical
Wiring, 20th edition, © Park Publishing, 2008, all rights reserved) A new form of fluorescent lighting offers a major breakthrough in terms of lower maintenance expense. The fluorescent lighting covered so far relies on electrodes within the lamp to initiate the arc
discharge that creates the energy to produce what is ultimately useful light. With few exceptions, electrodes have an electron-emitting coating, and when that wears off, the lamp is
burned out and must be replaced. What if there are no electrodes to burn out? Photographs
of Nikola Tesla in his laboratory, taken more than a century ago, show him holding long,
thin, sealed glass tubes coated internally with phosphors that produced light as he held them
in the air near a high-frequency source of power, of his invention, known today as a tesla
coil. Today the same process is being used to generate light, particularly in places for which
the maintenance expenses associated with relamping are high, such as street lighting.
Figure 10.51 shows a streetlight that works on this principle. The base contains provisions
to mount a photocell with the ballast out of sight behind it. The ballast is an induction
FIGURE 10.51 A decorative induction fluorescent streetlight. The lamp at the right, which has no
electrodes, should last 25 years. The inside contour of the glass envelope of the lamp, not visible in
this photo, is cylindrical in shape, extending vertically from its base almost to the top of the globe. It
fits perfectly over the exciter coil wound around the outside of the vertical section of the luminaire.
An attractive glass globe (not shown) completes the assembly.
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10.59
generator operating at about 2.6 MHz. The generator is connected via coaxial cable to the
axially located power coupler that serves as an antenna coil extending vertically out of the
top of the base. A special fluorescent lamp is at the right. It is in the shape of an incandescent lamp, but it contains a small amount of mercury and internal phosphors similar to conventional fluorescent lamps, giving 3000 or 4000 K white light, and it has a comparable
efficacy. The lamp has no electrodes to wear out. The light output from this 85-watt system
is initially 6000 lumens, falling to a mean of 4800 lumens, with a CRI above 80. The lamp
life is rated at 100,000 hours, which translates to about 25 years of evening streetlight duty.
Since relamping streetlights typically involves work from a bucket truck, this reduction in
maintenance overhead results in substantial savings.
This technology is available in other forms, with other lamp shapes and optics. For
example, there are doughnut-shaped lamps that fit into high-bay-style downlighting suitable for industrial and warehouse applications. These directly compete with comparable
HID luminaires. The principle of induction-coupled fluorescent light remains the same. For
these applications, there is another benefit. In addition to the lower maintenance expense,
there is no restrike time, so the lights can turn on and off at the flick of a snap switch, just
like fluorescent lighting in an office.
HIGH-INTENSITY-DISCHARGE LAMPS
112. High-intensity discharge lighting covers (Standard Handbook for Electrical
Engineers) a general group of lamps consisting of mercury, metal halide, and high-pressure
sodium lamps. A mercury lamp is an electric discharge lamp in which the major portion of
the radiation is produced by the excitation of mercury atoms. A metal halide lamp is an electric discharge lamp in which the light is produced by the radiation from an excited mixture
of a metallic vapor (mercury) and the products of the dissociation of halides (e.g., halides of
thallium, indium, sodium). A high-pressure sodium lamp is an electric discharge lamp in
which the radiation is produced by the excitation of sodium vapor in which the partial pressure of the vapor during operation is of the order of 106 N/m2, or about 10 atm.
A lamp designation system developed by the American National standards Institute
(ANSI) is currently in use. It consists of five groups of letters or numbers: first a letter indicating the type of lamp (H, mercury; M, metal halide; S, high-pressure sodium), followed
by an arbitrary number designating electrical characteristics (which relates to the type of
ballast required), followed by two arbitrary letters which describe the physical characteristics, then the lamp nominal wattage, and finally letters indicating the phosphor color. An
example for a 175-W metal halide lamp would be M57/C/175/U/MED.
113. High-intensity–discharge (HID) lamps (Standard Handbook for Electrical
Engineers) consist of a cylindrical transparent or translucent arc tube which confines the
electric discharge and the associated gases. That tube is further enclosed in a glass bulb or
outer jacket to exclude air to prevent oxidation of the metal parts and to stabilize operating
temperatures and significantly reduce ultraviolet radiation emitted by the excitation of the
vapors. The mount structure of many HID lamps is anchored to the “dimple top” of the
outer glass bulb, ensuring greater structural integrity and more accurate alignment of
the arc tube. The construction of a typical mercury lamp is shown in Fig. 10.52. The basic
elements are the arc tube, fabricated from fused silica and filled with a drop of mercury and
a rare gas at low pressure; the electrodes; and the outer envelope, which may or may not have
a phosphor coating on the interior for improved color rendering. Mercury lamps, due to their
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ELECTRIC LIGHTING
10.60
DIVISION TEN
relative inefficiency and generally poor color
rendering, are rarely, if ever, applied in today’s
lighting designs. They will be covered here
because many are still in service. Refer to Fig.
10.24 and the caption thereto for the usual shape
designations that apply to HID lamps.
114. The high-pressure mercury lamp
consists of a quartz arc tube sealed within an
outer glass jacket or bulb. The inner arc tube is
made of quartz to withstand the high temperatures resulting when the lamp builds up to normal wattage. Two main electron-emissive
electrodes are located at opposite ends of the
tube; these are made of coiled tungsten wire.
Near the upper main electrode is a third, or
starting, electrode in series with a ballasting
resistor and connected to the lower mainelectrode lead wire.
FIGURE 10.52 Mercury lamp.
The arc tube in the mercury lamp contains a
small amount of pure argon gas which is used
as a conducting medium to facilitate the starting of the arc before the mercury is vaporized.
When voltage is applied, an electric field is set up between the starting electrode and the
adjacent main electrode. This ionizing potential causes current to flow, and as the main arc
strikes, the heat generated gradually vaporizes the mercury. When the arc tube is filled with
mercury vapor, it creates a low-resistance path for current to flow between the main electrodes. When this takes place, the starting electrode and its high-resistance path become
automatically inactive.
Once the discharge begins, the enclosed arc becomes a light source with one electrode
acting as a cathode and the other as an anode. The electrodes will exchange functions as the
ac supply changes polarity.
The quantity of mercury in the arc tube is very carefully measured to maintain quite an
exact vapor pressure under design conditions of operation. This pressure differs with
wattage sizes, depending on arc-tube dimensions, voltage-current relationships, and various
other design factors.
Efficient operation requires the maintenance of a high temperature of the arc tube. For
this reason the arc tube is enclosed in an outer bulb made of heat-resistant glass, which
makes the arc tube less subject to surrounding temperature or cooling by air circulation.
About half an atmosphere of nitrogen is introduced in the space between the arc tube and
the outer bulb. The operating pressure for most mercury lamps is in the range of 2 to 4 times
atmospheric pressure. Lamps can operate in any position. However, light output is reduced
when burned in position other than vertical. Mercury lamps for lighting applications range
in wattage from 40 to 1000 W. The 175- and 400-W types are the most popular. Mercury
lamps are used in street lighting, industrial lighting, and outdoor area lighting. In new
installations today, mercury lamps are being replaced with more efficient metal halide or
high-pressure sodium systems. A typical clear mercury lamp is shown in Fig. 10.52. Some
special mercury lamps are available for use in ultraviolet applications.
115. Phosphor-coated mercury lamps are the most widely used mercury lamps.
Within the visible region the mercury-lamp spectrum, or energy radiated, consists of principal wavelengths. The lack of radiation in the red end results in a greenish-blue light.
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10.61
When one looks at a lighted mercury lamp,
the source itself appears to emit a daylight
white. The absence of red radiation causes
most colored objects to appear distorted in
color value. Blue, green, and yellow colors of
objects are emphasized, while orange and red
objects appear brownish or black.
Color improvement has been incorporated
in the design of mercury lamps by the use of
special phosphors on the inside of the outer
bulb (Fig. 10.53). The function of the phosphor
is to convert the invisible ultraviolet energy
into visible light in the same manner as light is
produced in fluorescent lamps. The phosphor FIGURE 10.53 Phosphor-coated mercury lamp.
produces light principally in the red region, [General Electric Co.]
where the light from the arc tube is deficient.
The original color-improved phosphors provided better color appearance with a small loss in
lamp efficacy. Present phosphor-coated mercury lamps utilize a vanadate phosphor which not
only significantly improves color appearance but increases lamp efficacy over clear mercury
lamps by 7 to 11 percent. Most phosphor-coated mercury lamps provide a cool tone of light
output somewhat similar to cool-white fluorescent lamps. Lamps are also available with a
phosphor that creates a warmer tone of light output close to that of incandescent lamps.
116. Metal halide lamps are similar to mercury lamps in construction, in that the
lamp consists basically of a quartz arc tube mounted within an outer glass bulb. However, in
addition to mercury, the arc tubes contain halide salts, usually sodium and scandium iodide.
During lamp operation, the heat from the arc discharge evaporates the iodides along with the
mercury. The result is an increase in efficacy approximately 50 percent higher than that of a
mercury lamp of the same wattage together with excellent color quality from the arc.
The amount of the iodides vaporized determines lamp efficacy and color and is
temperature-dependent. Metal halide arc tubes have carefully controlled seal shapes to maintain temperature consistency between lamps. In addition, one or both ends of the arc tube are
coated to maintain the desired arc-tube temperature. There is some color variation between
individual metal halide lamps owing to differences in the characteristics of each lamp.
(Standard Handbook for Electrical Engineers) Metal halide lamps have historically been
susceptible to color maintenance problems due to shifts in their color over time. Recent
developments aimed to minimize the occurrence of this problem include special roundedshape arc tubes, pulse start ignitor technology, and the use of ceramic arc tubes. Another relatively new technology is that of ceramic arc-tube metal-halide lamps. These lamps are
generally available in the lower wattages, some in PAR shapes, and provide improved color
consistency and very good color rendering. The clear arc tube is replaced with a short
translucent ceramic arc tube of similar material to that used in a high-pressure sodium lamp.
Metal halide lamps utilize a starting electrode at one end of the arc tube which operates in the same manner as the starting electrode in a mercury lamp. A bimetal shorting
switch is placed between the starting electrode and the adjacent main electrode. This
switch closes during lamp operation and prevents a small voltage from developing
between the two electrodes, which in the presence of the halides could cause arc-tube seal
failure. A typical metal halide lamp is shown in Fig. 10.54, and Fig. 10.55 is a drawing
with the parts identified.
Metal halide lamps are available in 32-, 50-, 70-, 100-, 175-, 250-, 400-, 1000-, and
1500-W sizes. There are also special halide lamps with limitations in burning positions
which have higher lamp efficacy. While many metal halide lamps can be operated in any
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10.62
DIVISION TEN
FIGURE 10.54
Metal halide lamp. [General Electric Co.]
Getter cup
Spacer
Upper support
Arc tube strap
End paint
Return lead
Envelope
BT 37
Arc tube
Electrode
Connector
lead
Lower support
Stem
Base
FIGURE 10.55 Construction of a standard metal halide lamp. (Courtesy of
Osram Sylvania.)
burning position, initial light output, lumen maintenance, and life ratings change with burning position. There are also 175-W and 400-W metal halide lamps designed for special
metal halide regulator type ballasts which provide higher lamp efficacy and longer life.
Although metal halide ballasts are designed to the specific starting and operating requirements for these lamps, there are several metal halide lamps which are designed to operate on
certain 400- or 1000-W mercury-lamp ballasts. They provide substantially higher light output over life than the mercury lamps they have replaced. Special 250-W and 400-W metal
halide lamps are available to operate on comparable wattage high pressure sodium ballasts.
These lamps are intended for use in applications where the color of HPS lamps is not desired.
Light output and life of the metal halide lamps is lower than with the HPS lamps.
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10.63
Phosphor-coated metal halide lamps have the same external appearance as phosphorcoated mercury lamps. They are available in 175-, 250-, 400-, and 1000-W types. Although
the light from the metal halide arc tube provides good color rendition, the phosphor,
similarly to phosphors used in mercury lamps, adds further to the color rendition. It also
provides a diffuse light source for lighting fixtures when optical characteristics are better
suited to this type of lamp. Special metal halide lamps, with aluminized reflective coatings
on the top of the bulb, can reduce glare and help minimize light trespass. There are PARand R-bulb mercury and metal halide lamps, xenon metal halide for fiber optic systems, and
iodine metal halide to simulate natural daylight.
117. The ultraviolet energy produced by mercury and metal halide arc tubes is
absorbed by the outer bulb in normal operations. However, in the event that the outer bulb
is broken by being struck by an external object such as a basketball in a gymnasium, the arc
tube, if not damaged, may continue to operate for many hours. With sufficient exposure,
the ultraviolet energy from an arc tube operating without the protection of the outer bulb
can cause temporary sunburn of the skin or eyes, similar to an excess exposure to the sun.
For lighting applications in open fixtures where lamps may be subject to accidental or
intentional breakage, special self-extinguishing lamps are available. These lamps are
designed with an internal fuse in series with the arc tube, which opens within 15 min when
exposed to air, causing the arc to be extinguished.
The NEC requires that in such facilities the luminaires installed be equipped with a solid
glass or plastic lens to provide containment. In addition, metal-halide lamps are known to
occasionally undergo what the industry euphemistically describes as “nonpassive end-oflife failures.” For this reason the NEC requires, regardless of location, that metal halide
luminaires using lamps other than thick-glass parabolic reflector (PAR) lamps must be
either contained or provided with a rejection feature so they can only be relamped with a
special type of lamp. These lamps, designated “Type O,” (for “open”), have been tested to
contain an inner arc-tube rupture and have a longer-than usual screw-shell. They mate with
a Type O lampholder, which is deep enough that any other metal-halide lamp will not be
able to be screwed in far enough to meet with the center contact, preventing energization.
118. The high-pressure sodium (commonly referred to as HPS) lamp has the highest
light-producing efficacy of any commercial source of white light (Fig. 10.56), with a drawing
showing its internal parts in Fig. 10.57. Like most other high-intensity–discharge lamps, highpressure sodium lamps consist of an arc tube enclosed within an outer glass bulb. The arc operates in a sodium vapor at a temperature and pressure which provide a warm color with light in
all portions of the visible spectrum at a high efficacy. Owing to the chemical activity of hot
sodium, quartz cannot be used as the arc-tube material. Instead, high-pressure sodium arc tubes
are made of an alumina ceramic (polycrystalline alumina oxide) which can withstand the corrosive effects of hot sodium vapor.
There are coated-tungsten electrodes sealed at each end of the arc tube. The sodium is
placed in the arc tube in the form of a sodium-mercury amalgam which is chemically inactive. The arc tube is filled with xenon gas to aid in starting.
High-pressure sodium lamps are available in sizes from 35 to 1000 W. They can be
operated in any burning position and have the best lumen-maintenance characteristic of the
three types of HID laps. Except for the 35-W lamp, most high-pressure sodium lamps have
rated lives of more than 24,000 h. The 35-W lamp has a rated life of 16,000 h. The 50-,
70-, 100-, and 150-W sizes are available in both a mogul-base and a medium-base design.
Diffuse-coated high-pressure sodium lamps are available in several wattages for use in
lighting fixtures where a larger effective light-source size is desired, such as units for low
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10.64
DIVISION TEN
FIGURE 10.56
High-pressure sodium lamp. [General Electric Co.]
mounting height and decorative applications. The coating
does not change the lamp color and reduces lamp efficacy by
5 to 7 percent.
Improved-color high-pressure sodium lamps are available
in a few types with significantly better color appearance. This
is achieved through a change in arc-tube pressure. The light
output and life of improved-color HPS lamps are less than
with the standard high-pressure sodium lamp.
Special high-pressure sodium lamps have been designed
to operate on specified mercury ballasts. Lamp design is similar to that of standard high-pressure sodium lamps except
that a neon-argon starting gas is used and an internal starting
aid is located in the lamp to permit starting on approved mercury ballasts. These lamps can only be used on reactor or
autotransformer lag-type mercury ballasts. Lamp life and
efficacy are reduced for these special HPS lamps.
FIGURE 10.57 Construction
of a typical high-pressure
sodium lamp. (Courtesy of
Osram/Sylvania.)
119. HID spectral-distribution mercury, metal halide,
and high-pressure sodium lamps have significantly different
color characteristics in the light produced by each type. All
HID lamps produce light in definite lines or bands rather than
the continuous spectrum of an incandescent lamp. The typical
spectral-power-distribution curves for HID lamps are shown
in Fig. 10.58.
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ELECTRIC LIGHTING
10.65
FIGURE 10.58 Spectral characteristics of high-intensity–
discharge lamps. [General Electric Co.]
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ELECTRIC LIGHTING
10.66
DIVISION TEN
FIGURE 10.58
(Continued )
120. Application of HID lamps for general lighting. HID lamps are widely used in
flood-lighting and roadway, industrial, and sports lighting and to an increasing extent in
indoor commercial applications. Owing to their greater efficacy, metal halide and highpressure sodium lamps have replaced mercury lamps in new HID installations. In addition,
many mercury installations are being changed to metal halide or HPS systems. Mercury
lamps are used today primarily for replacement purposes.
HPS lamps are used predominantly in applications where efficacy and lowest lightingsystem operating costs are the primary factors affecting system choice. Metal halide systems are used primarily in installations where color appearance together with high
efficiency are important, such as store applications or sports lighting for television.
121. Reflector-type mercury lamps are available in several wattages for use in
applications where it is desirable to provide optical control of the light within the lamp. As
in the case of incandescent reflector-type lamps, the sealed-in reflecting surface does not
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ELECTRIC LIGHTING
10.67
deteriorate during the life of the lamp. Reflector-type lamps are available in 100-, 175-,
250-, 400-, and 1000-W sizes. They are used primarily in floodlighting applications.
Typical types are shown in Fig. 10.59.
FIGURE 10.59
Reflector-type mercury lamps. [General Electric Co.]
122. Self-ballasted mercury lamps. All mercury lamps require a ballast to provide
proper starting voltage and control the current in the lamp. Self-ballasted mercury lamps
are lamps which will start with the available line voltage and contain an internal tungsten
filament in series with the arc tube to limit the lamp current. The filament ballast increases
the losses in the lamp. Thus, the lamp efficacy of self-ballasted mercury lamps is much
lower than that of other mercury lamps. Since there is no ballast in the circuit, self-ballasted
mercury lamps, like incandescent lamps, must be matched to the voltage at the socket.
123. High-intensity–discharge lamp ballasts. (Standard Handbook for
Electrical Engineers) The practical limit of an HID lamp’s current-carrying capacity is how
high a temperature its enclosing tube can withstand without rupturing. By connecting an
impedance in series with the lamp, the current is controlled. In most lamps about one-half
the supply voltage is absorbed by a series ballasting device. As a result, unless a currentlimiting device is used, the lamp current will increase until the lamp is destroyed. Ballasts
for HID lamps provide three basic functions: to control lamp current to the proper value, to
provide sufficient voltage to start the lamp, and to match the lamp voltage to the line
voltage. Ballasts are designed to provide proper electrical characteristics to the lamp over
the range of primary voltage stated for each ballast design. Most HID ballasts are designed
into the luminaire. Typical ballasts are shown in Fig. 10.60.
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10.68
FIGURE 10.60
DIVISION TEN
Ballasts for high-intensity– discharge lamps. [General Electric Co.]
Ballasts are classified into three major categories depending on the basic circuit
involved: nonregulating, lead-type regulating, and lag-type regulating. Each type has different operating characteristics.
Circuits for mercury-lamp ballasts are shown in Fig. 10.61. Reactor ballasts can be used
if sufficient line voltage is available to start and operate the mercury lamp, approximately
twice the lamp voltage. These ballasts have a low power factor unless corrected by a capacitor. The lag ballasts consists of an autotransformer plus a reactor combined in a single
structure. Performance is similar to that of a reactor, and the ballast is used where normal
line voltage is lower than the required lamp-starting voltage. This ballast also has a low
power factor unless corrected by a capacitor. Lag and reactor ballasts should only be used
when line-voltage regulation is good, not over 5 percent since lamp wattage will vary
10 percent with a 5 percent change in line voltage.
The regulator ballast, also referred to as the constant-wattage (CW) or stabilized ballast,
has primary and secondary windings electrically isolated from each other. A capacitor is
used together with the magnetic portion of the ballast to control the lamp current. Owing to
the capacitor, regulator ballasts have a high power factor. The basic advantage of regulator
ballasts is their excellent regulation of lamp wattage with changes in line voltage. Lamp
watts vary only 2 to 3 percent with line-voltage changes of 13 percent.
Autoregulator ballasts combine an autotransformer with the regulator circuit. As a
result, these ballasts are smaller and less costly than the regulator design and have lower
losses. They are also called constant-wattage–autotransformer (CWA) ballasts. The regulation of lamp wattage with line voltage is very good although somewhat less than with the
regulator design: approximately a 5 percent change in lamp wattage with a 10 percent
change in line voltage. Autoregulator ballasts have a high power factor. Multiple primaryvoltage ratings are available by using a series of taps in the transformer. Ballasts designed
for 120/208/240/277 V are available.
Two-lamp mercury-lamp ballasts are available. The circuit is basically the same as that
of the single-lamp regulator ballasts except that two lamps are operated in series.
Metal halide ballasts use the same circuit as mercury autoregulator ballasts. The magnetic design is different to provide the required peaked open-circuit voltage for satisfactory
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FIGURE 10.61
Co.]
10.69
Mercury-lamp ballast circuits. [General Electric
lamp starting and operation. Metal halide ballasts provide a regulation of lamp wattage
between those of an autoregulator and a reactor or lag ballast. With a 10 percent change in
low voltage, lamp wattage will vary by about 10 percent. All-metal-halide ballasts have a
high power factor.
Ballasts for high-pressure sodium lamps, in addition to providing the basic functions of
all ballasts, have an additional requirement. In contrast to mercury and metal halide lamps,
the voltage of high-pressure sodium lamps increases significantly during lamp life. The ballast must be able to handle this change and operate the lamp within specified limits. The
voltage required to start HPS lamps is much greater than that required for mercury and
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10.70
DIVISION TEN
metal halide types. This necessitates an auxiliary starting circuit which supplies a lowenergy, high-voltage pulse of several thousand volts. This starting aid is a separate device
from the magnetic and capacitor portions of the ballast. As the result of the high-voltage
starting pulse required by high-pressure sodium lamps, the lampholder for these lamps
must be rated to handle this voltage.
The circuits of high-pressure sodium ballasts are shown in Fig. 10.62.
FIGURE 10.62
Circuits of high-pressure sodium lamp ballasts. [General Electric Co.]
As with mercury reactor ballasts, reactor ballasts for high-pressure sodium lamps can be
used only when there is sufficient line voltage for proper lamp operation. They have a low
power factor, unless corrected, and have poor regulation of lamp wattage with line-voltage
variation. The required starting aid is part of the circuit.
Autoregulator and magnetic-regulator HPS ballasts are similar to mercury autoregulator and regulator ballasts, respectively, with the magnetic design changed to provide
the proper lamp characteristics and the addition of the starting aid. They have regulation
characteristics similar to those of mercury ballasts and have a high power factor.
As indicated with the various ballast designs, the ability of the ballast to control
lamp wattage and thus light output as the line voltage changes is referred to as lampwattage regulation. The effect of line-voltage variation on lamp wattage for the various
HID ballast designs is shown in Fig. 10.63.
Data on HID ballasts can be obtained from ballast manufacturers.
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ELECTRIC LIGHTING
FIGURE 10.63
Electric Co.]
10.71
Effect of line-voltage variation on HID lamps. [General
124. HID lamp warm-up and restrike. All high-intensity lamps require time for
the arc to stabilize as its operating value and achieve full light output. This requires several
minutes and is controlled by the ballast type. During the warm-up period, ballast line current and wattage will change continuously until they reach the stable operating point.
Figure 10.64 shows the characteristics for a typical lag autotransformer or reactor ballast
and a regulator ballast.
125. Low voltage-dip tolerance. The ability of an HID lamp to tolerate a dip in line
voltage depends on ballast design. Ballasts are usually rated on their ability to tolerate dips
of up to 4 s while keeping a lamp operating. Generally, nonregulating ballasts will tolerate
dips of only 10 to 20 percent, while regulating ballasts will sustain lamp operation during
dips in line voltage of as much as 30 to 50 percent for lag-type regulator ballasts and 20 to
40 percent for lead-type regulator ballasts. However, in HPS systems ballast dip tolerance
changes over time owing to the increase in lamp voltage. After midlife of the lamp, regulating and lead types of regulator ballasts become susceptible to lamp dropout with more
than 10 to 15 percent dips in line voltage. Dip tolerance of lag-type regulator HPS ballasts
also changes but remains above the tolerance for lead-type regulator ballasts.
When HID lamps are extinguished owing to a voltage dip or turning the fixture off, there
is a delay in restrike time until the arc tube can cool and internal pressure can drop to the
level where the arc will restrike with the available voltage from the ballast. This time varies
with different HID lamps. Mercury lamps will restrike in 3 to 7 min depending on the type.
Metal halide lamps can take as long as 15 min to restrike, while high-pressure sodium
lamps will restrike in the shortest time, usually within 1 min.
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ELECTRIC LIGHTING
10.72
DIVISION TEN
FIGURE 10.64 HID-lamp light output, lamp wattage, and line
current during the lamp warm-up period.
(Standard Handbook for Electrical Engineers) Tungsten-halogen auxiliaries are available
for HID industrial luminaires to provide standby illumination in the event of momentary
power failure. For indoor and outdoor sports lighting, and other applications where instant
restrike is preferable, special ignitors are available, as are special instant-restrike highpressure sodium lamps. Metal halide lamps with a wire lead (at the end opposite the base) are
used with auxiliary ignitors to achieve instant restrike. For aisle lighting in warehouses and
other interior and exterior situations where illumination levels for accurate seeing are not
needed all of the time, high/low electrical components, combined with occupancy detectors,
transmitters, and luminaire-mounted receivers can provide major energy saving by reducing
input wattage 50% to 70% during intervals when the spaces are unoccupied.
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ELECTRIC LIGHTING
10.73
126. Line fusing of HID ballasts. There are times when line fusing of an HID ballast may be desirable, as in high-bay or other relatively inaccessible installations. The principal reason for fusing is to remove a faulty luminaire from a circuit before it causes a
branch-circuit outage. A fused ballast aids in troubleshooting when a faulty ballast is
encountered. Fuse ratings should meet ballast manufacturers’ recommendations. Slowblow types are desirable when available to minimize nonfault opening.
127. Remote installation of HID ballasts. Although most HID lighting fixtures
have the ballast installed in the fixture, in occasional applications it is desirable to install
the ballast remote from the fixture. With mercury and metal halide systems, correctly sized
wire is required to maintain proper ballast voltage at the lamp socket as the primary design
factor. In HPS systems, the maximum distance is limited by the characteristics of the starting aid which provides the low-energy starting pulse. The ballast manufacturer should be
consulted for the remote-mounting distance limitation of HPS ballasts.
128. Effect of temperature. Excessive temperatures can result in lamp failure or
unsatisfactory performance. Most HID lamps have a maximum bulb-temperature limit of
400C (752F) and a maximum base-temperature limit of 210C (410F) for mogul-base
types and 190C (374F) for medium-base designs.
Most HID ballasts have sufficient voltage to start lamps at 29C (20F). HID ballasts
have maximum operating-temperature limits for reliable life performance. Ballasts
designed for mounting within fixtures have a coil-temperature limit of 165C (329F).
Enclosed ballasts are generally designed for ambient temperatures of 40C (104F) or less.
Special high-temperature enclosed-ballast designs are available for some lamp types for
ambient temperatures as high as 60C (140F).
129. High-intensity–discharge system troubleshooting. HID lighting systems
include the power supply system (wiring, circuit breakers, and switches), lighting fixture
(socket, reflector, refractor or lens, and housing), ballast, lamp, and, in outdoor fixtures, frequently a photoelectric cell to turn on the fixture at dusk. When an HID system does not
operate as expected, the source of the problem can be in any part of the total system.
It is important to understand normal lamp-failure characteristics to determine whether or
not operation is abnormal. All HID lamps have expected lamp-failure patterns over life; these
are published by lamp manufacturers. Rated life represents the expected failure point for onethird to one-half of the lamps, depending on the lamp type and the lamp manufacturer’s rating.
End-of-life characteristics vary for the different HID lamp types.
1. Mercury. Normal end of life is a nonstart condition or very low light output resulting
from blackening of the arc tube owing to electrode deterioration during life.
2. Metal halide. Normal end of life is a nonstart condition resulting from a change in the
electrical characteristic so that the ballast can no longer sustain the lamp. Lamp color at
the end of life will usually be warmer (pinker) than that of a new lamp owing to arc-tube
blackening during life that changes thermal balance in the arc tube. Metal halide lamps
can have a nonpassive failure mode at the end of life. This varies with lamp type and
burning position. The lamp manufacturer’s recommendations regarding metal-halide
lamp enclosure should be reviewed.
3. High-pressure sodium. Normal end of life is on-off cycling. This results when an aging
lamp requires more voltage to stabilize and operate than the ballast is able to provide.
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ELECTRIC LIGHTING
10.74
DIVISION TEN
When the lamp’s normally rising voltage exceeds the ballast output voltage, the lamp is
extinguished. Then, after a cool-down period of about 1 min, the arc will restrike and the
cycle is repeated. This cycle starts slowly at first and increases in frequency, if the lamp
is not replaced, until ultimately the lamp fails owing to overheating of the arc-tube seal.
There are four basic visual variations in the lamp of an HID lighting system which indicate that a problem may exist: (1) the lamp does not start, (2) the lamp cycle is on and off
or is unstable, (3) the lamp is extra bright, or (4) the lamp is dim. The following table indicates the most likely possible causes for each of these system conditions.
Possible causes
HID-system conditions
Lamp does not start.
Lamp cycle is on and off or
is unstable.
Lamp is extra bright.
Lamp is dim.
Other than lamp
Ballast failure
Incorrect or loose wiring
Low supply voltage
Low ambient temperature
broken
Circuit breakers tripped
Inoperative photocell
Starting-aid failure
(HPS)
Low supply voltage
Incorrect ballast
High supply voltage (HPS)
Ballast voltage low
System voltage dipping
Fixture concentrating
energy on lamp (HPS)
Shorted or partially
shorted ballast or capacitor
Overwattage operation
Low supply voltage
Incorrect ballast
Low ballast voltage to lamp
Dirt accumulation
Ballast capacitor shorted
Corroded connection in fixture
Lamp
Lamp loose in socket
Incorrect lamp
Normal end of life
Lamp internal structure
broken
Normal end of life or
or (HPS)
Lamp operating voltage
too high (HPS)
Lamp arc tube unstable
Incorrect lamp
High lamp voltage
Incorrect lamp
Low lamp voltage
Lamp a hard starter
130. Low-pressure sodium lamps (Fig. 10.65) utilize sodium vapor to conduct the
arc. They provide very high efficacy with light that is almost totally yellow in color. The lamps
are constructed with two glass envelopes. The inner arc tube is usually U-shaped and is made
of a special sodium-resistant glass. Glass can be used in low-pressure sodium lamps because
the sodium vapor operates at temperatures and pressures substantially lower than those of a
high-pressure sodium lamp. Electrodes are sealed into the ends of the arc tube. The arc tube is
filled with a starting gas of neon with a small amount of argon. Sodium metal is placed in the
arc tube. To reduce heat loss, the outer jacket is evacuated and the inside of the outer bulb is
coated with an indium oxide coating that transmits light but reflects infrared energy. Lowpressure sodium lamps are available in wattages from 18 through 185 W. As with any other
discharge lamp, low-pressure sodium lamps must be operated on a ballast designed to meet the
lamp-starting and -operating requirements. Owing to the monochromatic yellow color of the
light (consisting of a double line in the yellow region of the spectrum at 589 and 589.6 nm)
from low-pressure sodium lamps, they are generally used in applications where the appearance
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ELECTRIC LIGHTING
FIGURE 10.65
10.75
Low-pressure sodium lamp. [General Electric Co.]
of people and colors is not important. The major application of these lamps is for area lighting
and streetlighting where monochromatic yellow light is acceptable and a high luminous efficacy is required. Low-pressure sodium lamps are often applied in the vicinity of astronomical
observatories, since the monochromatic light can be filtered out of telescope images.
LIGHT-EMITTING DIODES (LEDS)
131. Light-emitting diodes (LEDs) represent a major new area of development in the
evolution of artificial illumination. Formerly reserved for low-power signaling, they are
steadily gaining power and whiteness to take their place as a source of conventional lighting.
An LED is a semiconductor diode that gives off light when voltage is applied so as to electrically bias the p-n junction (refer to Div. 6, Sec. 6 and Sec. 11 for details of how this works) in
the forward direction. Conventional diodes, such as those made from silicon or germanium, do
not radiate in this process, but some materials such as gallium arsenide do emit visible light.
LEDs inherently radiate incoherently but in a narrow spectrum, and as such are useful as indicators. Recently, however, methods have been found to produce white light from this process.
One approach is to sandwich an indium gallium nitride (InGaN) semiconductor in a cladding
layer of gallium nitride (GaN). The InGaN radiates at about 460 nm (dark blue) and the GaN
emits in the green range. If this combination is covered with a phosphor in the yellow range
(typically yttrium aluminum garnet crystals doped with trivalent cerium (Ce:YAG) the blue
light combines with the yellow from the phosphor. Since yellow is a combination of red and
green, the eye perceives the resulting mix as red, green, and blue, which makes a very passable
approximation of white. There are other approaches under active investigation, including the
use of nanotechnology to apply special coatings to blue LEDs.
The efficacy of white LED light sources has been steadily moving forward as well. The
highest efficacy commercially available is somewhat over 100 lm/W, which equals or
exceeds a very good fluorescent source and approaches the best high-pressure sodium
sources. This is a fast-moving target, and values even higher than this have been claimed in a
number of research facilities. The absolute theoretical maximum for any source is 683 lm/W;
this is the coefficient of the definite integral that defines luminous flux (see Sec. 15.)
NEON LAMPS
132. High-voltage neon lamps (Fig. 10.66) consist of two terminals or electrodes
set into the opposite ends of a glass tube which contains neon, helium, or argon gas, with
or without mercury, at low vapor pressure. Refer to Div. 9, Sec. 460 for NEC requirements
that pertain to this work. Refer to Sec. 141 for information on low-voltage neon lamps,
referred to as glow-lamps.
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ELECTRIC LIGHTING
10.76
DIVISION TEN
FIGURE 10.66 Schematic diagram of gas-filled tube and transformer. [S. C.
Miller and D. G. Fink, Neon Signs.]
As in all gaseous-discharge lamps a higher voltage is required to start the arc than is
required for continuous operation. These lamps are supplied from a high-reactance transformer in which the secondary voltage falls rapidly as the current drain is increased. This
feature provides the higher voltage required to start the lamp and tends to make the arc circuit stable. Even if the secondary terminals should become short-circuited, no more than
full-load current will flow, so that the transformer will not be damaged. A high voltage,
2000 to 15,000 V depending on the length and diameter of the tubing and the gas used, is
applied to the electrodes at the ends of the tubing by means of this transformer. Refer to
Div. 9, Sec. 459 and related sections for NEC requirements that apply to this transformer.
The tubing can be made to produce a number of different colors, depending on the gas
used, the color of the glass tubing, and whether or not mercury is added. Table 133 gives
the colors available.
133. Colors Obtainable from Neon Tubes
(From S. C. Miller and D. G. Fink, Neon Signs)
Color produced
Gas used
Mercury
used
Color of glass
tubing used
Gas pressure,
mm of mercury
Standard colors
Red
Dark red
Gold
White
Light green
Medium green
Light blue
Dark blue
Neon
Neon
Helium
Helium
Argon
Argon
Argon
Argon
No
No
No
No
Yes
Yes
Yes
Yes
Clear
Soft red
Soft yellow (noviol)
Clear
Soft canary (uranium oxide)
Soft yellow (noviol)
Clear
Soft blue
10 and over
10 and over
3
3
8
8
8
8
Colors available but not widely used
Soft red
Orange
Soft white
Dark green
Red lavender
Neon
Neon
Helium
Argon
Neon
No
No
No
Yes
No
Soft opal
Soft yellow (noviol)
Soft opal
Soft medium amber
Soft dark purple
10 and over
10 and over
3
8
10 and over
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ELECTRIC LIGHTING
10.77
ELECTRIC LIGHTING
134. The gas pressure as given in Table 135 must be determined quite accurately
during manufacture. If the pressure is too low, the resistance of the tubing and the cathode
voltage drop will be high and the tendency to sputter will be great. Sputtering means that
the metal of the electrode evaporates and deposits on the tube, causing the ends of the tube
to blacken. This process lowers the gas pressure still further until the tube flickers and
finally fails to light. If the pressure is too high, the light will not be brilliant. The gas pressure can be tested by holding a special type of spark coil (Fig. 10.67) against either the glass
or the electrode wire.
FIGURE 10.67 A high-tension spark coil for testing the vacuum system. The knob
at the end is used to control the intensity of the spark which appears at the metal tip
of the device. [S. G. Miller and D. G. Fink, Neon Signs]
135. Gas Pressure Determined by Color, Using Spark-Coil Tester
(S. C. Miller and D. G. Fink, Neon Signs)
Gas pressure,
mm of mercury
Coil held against
Color observed
Electrode wire
Purple
200
Electrode wire
Electrode wire
Electrode wire
Electrode wire
Electrode wire
Electrode wire
Glass
Glass
Glass
Glass
Purple
Purple
Blue purple
Red purple
Lavender
Light lavender
Dark blue
Light blue
Very light blue
Blue disappears
150
50
15
4
2
1
0.25
0.10
0.01
0.005
Remarks
Color visible only at edge of
electrode shell
Faint glow in tube
Fair glow in tube
Dark glow
No glow in tube, blue haze
near glass wall
136. The principal application of neon lamps is for sign lighting. They are
particularly adapted for this class of illumination owing to their bright colors and the fact
that the tubes lend themselves readily to the forming of letters and figures. The brilliant
single-color red, blue, or green light has an eye appeal in outdoor advertising which white
light cannot offer. The orange-red light of the neon tube penetrates great distances, making
neon signs stand out with brilliance and sparkle even on rainy nights. The flexibility of
these thin glass tubes in the forming of trademarks, special figures, and animated designs
also adds to their desirability to the advertiser. Finally, the relatively low wattage (about 4
to 6 W/ft of tubing) makes the operating cost relatively low.
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ELECTRIC LIGHTING
10.78
DIVISION TEN
137. The diameter of tubing used is from 7 to 15 mm (9/32 to 19/32 in). These
sizes are convenient to work with and thoroughly practical for almost all applications.
The voltage required per foot of tubing varies with the diameter of the tubing, as given
in Fig. 10.68. The smaller-size tubes give more brilliant light but require the greatest voltage
per foot of tube.
FIGURE 10.68 The voltage per foot required to
operate tubing of various diameters filled with neon
gas. [S. C. Miller and D. G. Fink, Neon Signs]
138. The transformers are rated according to secondary voltage and short-circuit
current in milliamperes. Table 140 gives a list of standard transformers with the length of
tubing in feet which can be supplied by each. This length varies with the diameter of the
tubing and the gas used. When it is desired to combine two different sizes and colors of tubing in series on one transformer, the chart of Fig. 10.69 can be used. Any combination of
lengths which are side by side in one column in the chart can be used on the transformer
whose rating is given above the chart.
For example, a 9000-V, 30-mA transformer may supply (in the first column of the chart)
20 ft (6.1 m) of 15-mm blue tubing and 16 ft (4.9 m) of 15-mm red or (in the third column)
20 ft of 15-mm red and 11 ft (3.4 m) of 12-mm blue, making a total of 36 ft (11 m) in the
first case of the larger tubing and 31 t (9.4 m) in the second case of the combination of
the larger and the medium-size tubing. Note that as the diameter of the tubing is decreased,
the number of feet which can be supplied decreases on account of the rise in the voltage per
foot, as shown in Fig. 10.73.
139. In the makeup of signs one section of tubing usually forms two or three letters. The different sections of tubes are then connected in series with wire jumpers until as
many feet of tubing have been assembled as can be handled by the transformer to be used,
as determined from Table 140. In large signs several transformers, each connected to its
own section of tubing, can be used. The crossovers of tubing between letters can be blocked
out by winding the tubing with tape and covering it with a waterproof varnish, or the tubes
can be painted with a nonmetallic opaque paint. The glass should be made perfectly clean
before painting by rubbing it with a wet cloth and drying. Metallic paint (with a lead or copper base) should never be used on the tubing, as it will conduct electricity and may cause a
corona discharge between the tube and the housing which will attack the glass.
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ELECTRIC LIGHTING
10.79
FIGURE 10.69 Chart for determining the footage of combinations of red and mercury tubing which may
be run from a single transformer. [S. C. Miller and D. G. Fink, Neon Signs.]
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ELECTRIC LIGHTING
10.80
DIVISION TEN
140. Transformer Chart, Showing Maximum Number of Feet of Tubing a
Given Transformer Will Carrya
(S. C. Miller and D. G. Fink, Neon Signs)
141. Low-voltage neon-glow lamps (Fig. 10.70) are operated on 105- to 125-V
dc or ac systems. They contain two plates to form electrodes spaced with their abutting
edges about 1/16 to 1/8 in (1.6 to 3.2 mm) apart. The bulb is filled with neon gas. A highresistance coil in the base or external is connected in series with the electrodes and serves
to limit the current, no auxiliary devices being necessary. When the circuit is closed, the
110 to 125 V causes the small air space between the plates to become ionized. A glow
FIGURE 10.70
Electric Co.]
Low-voltage neon-glow lamps. [General
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ELECTRIC LIGHTING
10.81
ELECTRIC LIGHTING
discharge takes place between the plates and then spreads so as virtually to cover the surface of the plates. The plates are very rugged and long-lived, failure usually being due to
the burning out of the series resistance. When these lamps are used on direct current, only
one electrode glows, whereas on alternating current both electrodes glow. They can therefore be used as an ac, dc detector device. They may be used as pilot and indicator lamps in
industry, for stroboscopic lamps in the laboratory, and as all-night lights in homes. Their
low wattage, long life, ad dependability make them ideal for such uses. Other glow-lamp
applications in electronic circuitry include oscillators, pulse generators. voltage regulators,
and coupling networks.The characteristics of neon-glow lamps are given in Table 142.
Their useful life varies approximately as the inverse of the cube of the current. A glow
lamp has a negative volt ampere characteristic; hence a limiting resistance is used in series
with it. In conventional screw-base types, the resistor is concealed in the base. Average
lamp life ranges between 7500 and 25,000 h.
142. Glow Lamps, 105–125 V
(General Electric Co.)
Lamp-ordering
code
Nominal
current,
mA
Bulb
Base
B1A (NE-51)
A1A (NE-2)
C7A (NE-2D)
0.3
0.7
0.7
T-31/2
T-2
T-2
A1H
1.2
T-2
C9A (NE-2J)
1.9
T-2
B5A(NE-17)
2.0
T-41/2
B7A (NE-45)
B8A (NE-47)
B9A (NE-48)
2.0
2.0
2.0
T-41/2
T-41/2
T-41/2
F3A (NE-57)
F4A (NE-58)b
J9A (NE-56)
J5A (NE-30)
2.0
2.0
5.0
12.0
T-41/2
T-41/2
S-11
S-11
Miniature bayonet
Wire leads
Single-contact
midget flange
Single-contact
midget flange
Single-contact
midget flange
Double-contact bayonet
candelabra
Candelabra screw
Single-contact bayonet
Double-contact bayonet
candelabra
Candelabra screw
Candelabra screw
Medium screw
Medium screw
Maximum
overall
length,
in
ac
dc
Series
resistance,
1 3/16
1
15/16
65
65
65
90
90
90
220,000
100,000
100,000
/8
95
135
47,000
15/16
11/2
95
65
135
90
30,000
30,000
1 17/32
11/2
11/2
65
65
65
90
90
90
30,000
30,000a
30,000
1 17/32
1 17/32
2 3/16
2 3/16
65
65
65
65
90
90
90
90
30,000a
100,000a
33,000a
7,500a
5
Starting
voltage
a
Internal resistor.
For 210- to 250-V applications.
b
143. Argon-glow lamps, which consist of a mixture of gases, radiate mainly blue
and violet and in the near-ultraviolet region. The negative glow appears blue violet. The
fact that there is strong radiation in the near-ultraviolet region can be demonstrated by the
fluorescent effects produced on uranium glass and many phosphorescent and fluorescent
substances. Commercially, therefore, argon-glow lamps are used to some extent as convenient ultraviolet sources.
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ELECTRIC LIGHTING
10.82
DIVISION TEN
ULTRAVIOLET-LIGHT SOURCES
144. Ultraviolet-light sources are lamps which are designed primarily to produce
light of wavelengths in the ultraviolet part of the spectrum (see Fig. 10.1). It should be
understood that not all ultraviolet light is the same. There are at present four recognized
bands of ultraviolet light. The band in which the light from any source falls depends upon
the wavelength of the light emitted. Each of the recognized bands differs widely from the
others in its characteristics, usefulness, and field of application. The four bands are as follows: the near-ultraviolet or fluorescent region, the erythemic region, the abiotic or bactericidal region, and the Schumann region. They are listed in order of decreasing wavelength
of the light, the wavelength of the near-ultraviolet being closest to that of visible light. The
light from the ordinary fluorescent lamp originates as its source as light in the nearultraviolet band. This nonvisible light is transformed into visible light by the fluorescence
of the coating on the lamp tube under the influence of the near-ultraviolet light. The light
output from the lamp therefore becomes visible light, so that the ordinary fluorescent lamp
is not an ultraviolet-light source. However, by the use of special phosphors for the coating
of fluorescent lamps, fluorescent lamps can be made to be sources of ultraviolet light.
The common methods of producing ultraviolet radiation are (1) by carbon and tungsten
arcs, (2) by tungsten filaments operated at higher temperatures than in ordinary lamps, and
(3) by gaseous-discharge lamps of proper design. Ultraviolet light can be used for healthful radiation as in the case of the sunlight lamps, for photographic printing, for illuminating fluorescent materials for analysis or for theatrical effects, or for the killing of germs as
in the case of the germicidal lamps.
145. Black light (General Electric Co.) is the popular name for near-ultraviolet radiant energy in the 320- to 380-mm range. The label is not a very precise one. Whether or not
this energy looks black is debatable. Certainly it is not light, because the human eye is
insensitive to it.
The interesting thing about black light is that when it falls on certain materials, it makes them
fluoresce, that is, emit visible light. What actually occurs is a conversion of energy: the black
light that falls upon the fluorescent surface is absorbed and then reradiated at longer wavelengths—wavelengths to which the eye is sensitive. So surfaces that contain or are treated with
fluorescent chemicals glow, white or in color, when irradiated by black light. If the surroundings are kept dark, as they often are, the effect is that of self-luminous elements floating in space.
The weirdly beautiful and dramatic effects that black light makes possible account for
its popularity in decoration, display, and advertising. In its many and rapidly expanding
workaday uses, black light makes it possible to see things that otherwise could not be seen.
The most important artificial sources of black light are black-light fluorescent and mercury lamps. All mercury lamps used for black-light applications require external filters.
Filament lamps are weak and inefficient sources of black light, and argon-glow lamps
produce it in only very small quantities. Carbon arcs produce useful amounts of black light.
Radiant energy from the sun and sky contains a strong black-light component.
Fluorescent black-light lamps are used in insect control. Many night-flying insects are
particularly sensitive to near-ultraviolet and blue light. Black-light lamps are used in insect
traps to attract the insects into the trap to be exterminated by an electric grid or trapped.
Tubular sources designated as BLB lamps, such as 4-, 6-, and 8-W T-5, 15-W T-8, and
20- and 40-W T-12 lamps, have integral filters and may be operated with the same ballasts
as corresponding fluorescent lamps. The luminance of an irradiated fluorescent material is
between 1 and 5 fL with printing inks and between 0.25 and 2.5 fL with interior paints,
depending on the color. The apparent brightness increases considerably as the eyes become
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ELECTRIC LIGHTING
10.83
ELECTRIC LIGHTING
dark-adapted. Conversely, the effectiveness of black light is greatly reduced or entirely
negated by a small amount of visible light.
Data for black-light lamps are given in Table 146.
146. Black-Light Lamps
(General Electric Co.)
Lampdesignation
Nominal
lamp
watts
Bulb
Base
Length,
ina
Related
average
life, hb
Approximate
relative blacklight energyc
6
6
9
12
18
18
24
24
18
24
48
48
72
6,000
6,000
7,500
7,500
7,500
7,500
9,000
9,000
7,500
12,000
20,000
20,000
12,000
4
3
6
8
25
20
42
31
40
90
100
81
190
71/2
57/16
57/16
57/16
81/4
7
71/2
81/4
115/16
24,000 18,000
12,000
12,000
24,000 24,000 24,000
24,000 24,000
68
68
18
18
120
30
30
165
270
Fluorescent lamps
F4T5/BL
F4T5/BLBd
F6T5/BLBd
F8T5/BLBd
F15T8/BL
F15T8/BLBd
F20T12/BL
F20T12/BLBd
F25T8/BL
F40BL/U/3
F40BL
F40BLBd
F72T12/BL/HO
4
4
6
8
15
15
20
20
25
40
40
40
85
T-5
T-5
T-5
T-5
T-8
T-8
T-12
T-12
T-8
T-12
T-12
T-12
T-12
Miniature bipin
Miniature bipin
Miniature bipin
Miniature bipin
Medium bipin
Medium bipin
Medium bipin
Medium bipin
Medium bipin
Medium bipin
Medium bipin
Medium bipin
Recessed
double-contact
Mercury lamps
HR100A38
HR100A38/A23
HR100PFL44/MED
HR100PSP44/MED
HR175A39
HR175RFL39
HR175RFL39/M
HR250A37
HR400A33
100
100
100
100
175
175
175
250
400
E-231/2
A-23
PAR-38
PAR-38
E-28
R-40
R-40
E-28
E-37
Mogul
Medium
Medium
Medium
Mogul
Medium
Mogul
Mogul
Mogul
a
Length of fluorescent lamps includes standard lampholders. Length of mercury lamps is the maximum overall
length.
b
Rated average life for fluorescent lamps is the life when operated at 3 h per start on ballasts meeting published
specifications. Rated average life for mercury lamps is the life when operated at 10 or more h per start on ballasts
meeting published specifications.
c
Relative value of 100 8100 fluorers.
d
Integral-filter lamp.
147. Filters (General Electric Co.). Most sources of black light produce visible light
along with the ultraviolet. In the great majority of applications this visible light is undesirable.
If it is not screened out by filters, it illuminates not only the luminous areas but also their surroundings. This, of course, reduces brightness contrasts and robs the display (or whatever the
application may be) of its effectiveness. So almost always some sort of light-absorbing filter
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10.84
DIVISION TEN
is placed between the black-light source and the irradiated surface. In the case of the BLB fluorescent lamps, the filter is an integral part of the lamp.
Filters having a wide range of characteristics are used for black-light applications. At
one extreme are filters that pass virtually no visible light and not very much ultraviolet; at
the other extreme are deep-blue sheet glasses that transmit appreciable visible light and a
great deal of near-ultraviolet. Scientifically designed black-light filters are regularly supplied in molded squares or roundels or in sheet glass. They are used in all black-light applications that require a high degree of absorption of the visible light. Some of the deep-blue
sheet glasses being used as black-light filters were not originally intended for this service.
But since their near-ultraviolet transmission is high, their cost is low, and they are easily
cut to any desired size, they are used in many applications in which some visible light can
be tolerated.
148. Applications of black light
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Decorative purposes in the lighting of murals and show-window displays
Insect control
Advertising: producing effects in outdoor signboards
Inspection of cast and machined parts
Detection of leaks in hydraulic systems
Diagnostic use in medicine and biology
Inspection of food
Inspection of textiles
Sorting of laundry via invisible markings
Checking cleanliness in restaurants, dairies, etc.
Photoproductive processes
Location of mineral deposits
149. Germ-killing or bactericidal lamps, called germicidal lamps (Fig. 10.71),
have been developed for use in many places for sterilizing and prevention of mold. The
germ-killing lamp is a gaseous-discharge lamp consisting of a long tube containing mercury vapor and inert gases. It gives out ultraviolet radiation in the bactericidal band which
kills bacteria of many kinds. Germicidal lamps are discharge lamps similar in operation to
fluorescent lamps and thus require the correct ballast for proper operation. Many germicidal lamps are designed to operate on standard fluorescent-lamp ballasts.
FIGURE 10.71
Germicidal lamps. [General Electric Co.]
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10.85
150. The uses for germicidal lamps
1. Storage and aging of meat. The meat when exposed to ultraviolet radiation can be kept
in a warm, high-humidity atmosphere where it will age and become tender much more
rapidly with no formation of mold or slime and with no loss of weight due to drying out.
2. Water sterilization.
3. Irradiation of air to prevent the spread of disease.
4. Sterilizing drinking glasses, hospital instruments, toilet seats, etc., to prevent the spread
of disease.
151. Photochemical lamps (General Electric Co.) are a family of mercury lamps
designed for specialized applications of ultraviolet radiation. The lamps with tubular quartz
bulbs transmit the full range of generated radiation. Since these emit shortwave germicidal radiation, they must be used with utmost caution. Bare tubes must not be exposed to the eyes or skin.
When lamps are used exposed, shortwave-absorbing glass filters should surround the lamp.
Ultraviolet radiation from quartz lamps is extremely useful as a catalyst in many industrial chemical processes such as polymerization, halogenation, chlorination, and oxidization. Similarly, the lamps are highly effective for ultraviolet therapy.
Quartz lamps are used by manufacturers for weathering tests on paints, dyes, and other
finishes. Since a high concentration of energy from lamps is possible, a few hours’ exposure may be equivalent to many days’ exposure to natural sunlight. These lamps have also
found widespread use in the sterilization of water. This method is particularly desirable
when the taste and odor from chemical sterilization are objectionable.
Photochemical lamps are used for black-and-white printing, blueprinting, copyboard
lighting, diazo printing, and vacuum-frame printing. Some lamps use an ultraviolettransmitting glass which does not transmit far ultraviolet. These are excellent photographic
lamps, since many of their strongest emission lines lie close to the maximum sensitivity of
most photosensitive materials.
INFRARED HEATING LAMPS
152. Heating or drying lamps are incandescent lamps with filaments which operate
at a lower color temperature (2500 instead of about 3000 K) so that most of the radiation
occurs in the infrared part of the spectrum with wavelengths longer than those of visible light.
Infrared lamps (Fig. 10.72) have many uses in commercial and industrial applications for
heating and drying and on farms for brooding of poultry and other animals. Important features
of these lamps include rapid heat transfer, efficient operation, simple oven construction, low
oven first cost, adaptability to conveyor-line production, cleanliness, and low maintenance
cost. The several wattages in each bulb size permit a wide range of temperatures.
The T-3 infrared quartz lamps are capable of delivering several times the energy concentration provided by the R-40 or G-30 types of lamps. They can be used in compact
trough reflectors for concentrated radiation.
153. Lamp Disposal. Fluorescent and other discharge lamps contain a relatively
small amount of mercury. For example, standard 4-ft fluorescent lamps contain about
20–30 mg of mercury. The amount in high intensity discharge (HID) lamps depends on the
lamp wattage. Mercury release into the environment is a concern. Small quantities of these
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10.86
FIGURE 10.72
DIVISION TEN
Infrared heating lamps. [General Electric Co.]
fluorescent or HID lamps placed in ordinary trash may not appreciably effect the nature or
method of disposal of the trash. However, under most circumstances disposal of large quantities of lamps may be regulated.
There are varying requirements regarding lamp disposal in different areas of the country,
and they may change.
Contractors and users disposing of quantities of fluorescent and HID lamps should be familiar with the regulations relating to lamp disposal in the geographic areas where they are working.
LUMINAIRES
154. Purpose of luminaires. A luminaire is a device which directs, diffuses, or modifies the light given out by the illuminating source in such a manner as to make its use more
economical, effective, and safe to the eye. The luminaire includes the reflector, lamp sockets, enclosing materials, ballasts in fluorescent and HID units, and stems and canopies where
used. Since the light from a bare lamp is given off approximately equally in all directions, to
use the light economically some accessory is required to direct the light to the desired areas.
As most lamps have a high brightness, it is desirable in producing satisfactory illumination
that the eye be shielded from the source in order to reduce direct glare. In many cases the
appearance of the illuminating system is of great importance, so that the luminaire must possess decorative features as well as those necessary for satisfactory illumination.
155. Distribution graphs of luminaires. The effect of a luminaire in changing the
direction and distribution of the light given out by a light source is best expressed by a distribution graph. Figure 10.73 shows such a graph for a bare lamp and for the same lamp
with a reflector. The graph represents the light in a single vertical plane through the center
of the light unit, and it is assumed that the light in all similar vertical planes are similarly
distributed. See Sec. 32, “How to Read a Photometric Graph.”
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10.87
FIGURE 10.73 Comparison between the distribution curve of a bare incandescent lamp and that of the
same lamp equipped with a suitable reflector.
Figure 10.74 shows a sample photometric test report for a 400-W HPS luminaire. A
report of this type is used in comparing luminaire with one another as to relative distribution of light, type of illumination, lumen-output efficiency, and brightness.
156. Classification of luminaires. Luminaires can be classified by several methods:
1. According to system of illumination produced
a. Direct
b. Semidirect
c. General diffuse or direct-indirect
d. Semi-indirect
e. Indirect
2. According to the amount that the luminaire encloses the lamp
a. Open
b. Enclosed
3. According to class of service
a. Industrial
b. Commercial and institutional
c. Residential
d. Street lighting
e. Floodlighting
4. According to the material used for reflection or transmission of the light
a. Steel
b. Aluminum
c. Opal glass
d. Prismatic glass
e. Glass and metal
f. Plastic
g. Plastic and metal
5. According to method of mounting
a. Suspended
b. Surface-mounted
c. Recessed or built-in
6. According to light source
a. Incandescent lamp
b. High-intensity–discharge lamp
c. Fluorescent lamp
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10.88
FIGURE 10.74
DIVISION TEN
Photometric test report. [General Electric Co.]
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10.89
157. Direct lighting is defined as a lighting system in which practically all (90 to
100 percent) of the light of the luminaries is directed in angles below the horizontal directly
toward the usual working areas (Fig. 10.75, VI). This type of lighting is produced by luminaires, which range from industrial-type steel or aluminum reflectors to fixtures mounted
above large light-source areas such as glass or plastic panels and skylights. Although, in
general, such a system provides illumination on working surfaces most efficiently, this
achievement may be at the expense of other factors such as excessive contrasts of the light
source with the surroundings, troublesome shadows, or direct and reflected glare.
(Standard Handbook for Electrical Engineers) The distribution may vary from widespread to highly concentrating, depending on the reflector material, finish, and contour, and
on the shielding or control media employed. Troffers and downlights are two forms of
direct luminaires. Direct lighting units can have the highest utilization of all types, but this
utilization may be reduced in varying degrees by brightness-control media required to minimize direct glare. Veiling reflections and shadows may be excessive unless the distribution and location of luminaires are designed to reduce these effects. Large-area units are
generally also advantageous since they soften shadows. Luminous ceilings, louvered ceilings, and large-area modular lighting elements are forms of direct lighting having characteristics similar to those of indirect lighting discussed in paragraphs below. Luminous
ceilings may be difficult to apply at low power densities.
158. Indirect lighting. From 90 to 100 percent of the light output of the luminaire is
directed toward the ceiling at angles above the horizontal (Fig. 10.75, I). Practically all the
light effective at the working plane is redirected downward by the ceiling and to a lesser
extent by the sidewalls. Since the ceiling is in effect of the light source, the illumination
produced is quite diffuse in character. While indirect lighting is not as efficient as some of
the other systems on a purely quantitative basis, the even distribution and absence of shadows and reflected glare frequently make it the most desirable type of installation for offices,
schools, and similar applications. Because room finishes play such an important part in
redirecting the light, it is particularly important that they be as light in color as possible and
carefully maintained in good condition. The ceilings should always have a matte finish if
reflected images of the light source are to be avoided.
Glass or plastic luminaires in this classification are known as luminous indirect, while
metal luminaires which transmit no light are totally indirect. The translucent type is sometimes more desirable than the totally indirect because a luminous fixture is less sharply silhouetted against the relatively bright ceiling. Indirect illumination may also be provided by
means of architectural coves. Luminaire suspension length, or cove proportions, must be
carefully selected to provide uniform ceiling coverage, where desired, and to prevent
excessive ceiling brightness.
159. Semi-indirect lighting. From 60 to 90 percent of the light output of the luminaire is directed toward the ceiling at angles above the horizontal (Fig. 10.75, II), while the
balance is directed downward. Semi-indirect lighting has most of the advantages of the
indirect system but is slightly more efficient and is sometimes preferred to achieve a desirable brightness ratio between ceiling and luminaire in high-level installations. The diffusing medium employed in these luminaires is glass or plastic of a lower density than that
employed in indirect equipment.
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10.90
DIVISION TEN
FIGURE 10.75
Systems of illumination.
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FIGURE 10.75
10.91
(Continued)
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10.92
DIVISION TEN
160. General diffuse or direct-indirect lighting. From 40 to 60 percent of the
light is directed downward at angles below the horizontal. The major portion of the illumination produced on ordinary working planes is a result of the light coming directly from the
luminaire. However, a substantial portion of the light is directed to the ceiling and sidewalls. If these are light in color, the upward light provides a brighter background against
which to view the luminaire, in addition to supplying a substantial indirect component
which adds materially to the diffuse character of the illumination. The difference between
the general diffuse (Fig. 10.75, III) and direct-indirect (Fig. 10.75, IV) classifications is in
the amount of light produced in a horizontal direction. The general diffuse type is exemplified by the enclosing globe which distributes light nearly uniformly in all directions,
while the direct-indirect luminaire produces very little light in a horizontal direction, owing
to the density of its side panels. Glass, plastic, or louvered bottoms are commonly used with
the latter type of luminaire to provide lamp shielding.
161. Semidirect lighting. From 60 to 90 percent of the light is directed downward
at angeles below the horizontal (Fig. 10.75, V). The footcandles effective under this system
at normal working planes are primarily a result of the light coming directly from the luminaire. The portion of the light directed to the ceiling results in a relatively small indirect
component, the greatest value of which is that is brightens the ceiling area around the luminaire, with a resultant lowering of brightness contrasts. Equipment of this type is exemplified by the suspended plastic-sided fluorescent luminaire or the open-bottom glass shade
for incandescent lamps.
162. An open luminaire is one which only partially encloses the lamp. Open directlighting luminaires have the lamp exposed to view from at least one direction. The luminaires of Figs. 10.78, 10.79, 10.81, I, and 10.82 III are open-type direct-lighting units.
163. An enclosed luminaire completely encloses the lamp from view from any
direction. The ones shown in Figs. 10.82, I, II, and IV, and 10.83 are enclosed direct-lighting
luminaires.
164. Classification of luminaires according to class of service. Industrial service refers to use in factories and manufacturing establishments. Commercial service refers
to use in offices, stores, and public buildings. Residential use means use in houses and
apartments; street lighting means the illumination of streets, roads, and highways; and
floodlighting means the illumination of outdoor areas such as painted signs, recreational
grounds, automobile parking spaces, and building exteriors.
165. Steel reflectors have a sheet-steel base coated with porcelain enamel, paint
enamel, or aluminum paint to form the reflecting surface. The best types of steel reflectors
are those coated with porcelain enamel, since their reflecting surface is very efficient,
durable, and easily cleaned. Paint-enamel reflectors when new are quite efficient, but the
reflecting surface deteriorates very rapidly. Aluminum-painted reflectors are slightly better than paint-enamel ones but not so durable as porcelain-enamel ones.
Steel reflectors are used in the manufacture of many luminaires of the direct and indirect
types.
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10.93
166. Aluminum reflectors are used in many different types of luminaires. The
reflecting surface is usually given an electrochemical treatment called Alzak which
removes the impurities from the aluminm and endows it with a hard, durable surface which
has a high reflection efficiency of approximately 90 percent. Like steel reflectors, aluminum reflectors are used in luminaires for both direct and indirect lighting.
167. Opal glass is a white diffusing glass (Sec. 10) which transmits light with a loss
of only about 15 to 35 percent, the amount depending on the density of the glass. It breaks
up the light rays so that the lamp is not visible and glare is kept at a minimum. Opal glass
is used for enclosed diffusing luminaires for incandescent and HID lamps and for sidepanel shields in some commercial fluorescent luminaires.
168. Prismatic glass consists of clear glass which is molded into scientifically
designed prisms. Each prism is designed with reference to the position of the light source.
By proper design, distribution curves of the extensive, intensive, or focusing types are
obtained. The extensive reflector or globe refractor distributes the light over a wide angle
below the horizontal (Fig. 10.76, I), the maximum intensity being at an angle of about 45
with the vertical.
Intensive reflectors, globes, and lenses (Fig. 10.76, II) throw the light directly downward, the maximum intensity occurring between 0 and 25 with the vertical.
FIGURE 10.76 Distribution characteristic curves for direct prismatic-glass luminaires. [Manville Special
Products Group, Holophane Division]
Focusing globes, lenses, and reflectors (Fig. 10.76, III) concentrate the light to a small
area, producing the greatest intensity of illumination along the axis of the reflector.
Focusing units give an end-on candlepower approximately 31/2 times as great as the rated
horizontal candlepower of the lamp. The area intensely illuminated is a circle, the diameter
of which should be one-half the height of the lamp above the plane of illumination; outside this limit the intensity falls rapidly but not so abruptly as to give the effect of a spot
of light. Generally focusing units give their maximum candlepowers at about 10 from
the vertical.
Prismatic-glass units are used in many direct, semidirect, and semi-indirect luminaires.
The different types of prismatic units employed are reflectors, globes, and lenses. Some
luminaires employ only a single type of unit, and others employ a combination of types of
units. Luminaires employing prismatic-glass units are available for incandescent, fluorescent, and HID lamps.
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10.94
DIVISION TEN
169. Combination glass-and-metal luminaires are used principally for enclosed
direct-lighting units. The metal part of the unit usually direct the light, while the glass is
used for diffusing purposes or simply for the enclosure of the unit so that it will be dusttight
or vaportight.
170. Plastics are used to some extent in luminaires for incandescent lamps and HID
lamps and to quite a great extent for fluorescent lamps. The incandescent luminaires
employing plastics are of the semi-indirect type (very close to indirect). With fluorescent
units plastic is used in many direct and direct-indirect luminaires for side-panel shielding.
It is also used quite extensively for bottom and side enclosures of direct and semidirect fluorescent units.
171. A combination of plastic and metal is used in some fluorescent luminaires.
In some units the plastic is used for side-panel shielding. In others it is used to enclose the
bottom of the unit for diffusing purposes or for making the unit dusttight and vaportight.
172. Method of mounting. Suspended mounting refers to hanging the luminaire
from the ceiling with a chain, tube, conduit, or cord-pendant suspension. Surface mounting refers to placing the body of the luminaire directly against the ceiling. Recessed or
built-in mounting refers to placing the luminaire in recesses in the ceiling or on the walls
or structural members, so that it forms a part of the architectural treatment of the building
interior.
173. Luminaires for use with incandescent lamps are available for all classes of
service. For a discussion of street-lighting and floodlighting equipment refer to Secs. 233
and 241. Incandescent luminaires for residential use are available in a great variety of types,
which are too numerous to be discussed here.
174. Industrial luminaires for incandescent lamps are of either the metal or the
glass-metal type. The more common types are discussed in the following sections.
175. Enameled-steel–reflector luminaires for incandescent lamps are made
in several different types of assemblies. One type has a reflector and hood pressed in one
piece. When the nut is loosened at the top, the reflector will slide up on the stem, exposing
the socket for wiring. This is a weatherproof type for use outdoors and for indoor installations where interchangeability of reflectors and ease of cleaning are not the important considerations. With the turn-lock type of reflector, the entire reflector and socket can be
removed from the supporting cap by a quarter turn and taken down for cleaning. The prongs
of the turnlocking device, in addition to supporting the reflector and socket, provide the
electrical connection from the socket to the circuit terminated in the cap. This type is especially advantageous in locations where the cleaning of reflectors in position is going to be
difficult. The threaded-reflector type has a reflector which can be removed from the socket
and hood by unscrewing. Several shapes of reflectors will fit the same hoods. Hoods are
available with a threaded connection for fixture-stem suspension or with a flange having
holes for mounting as the cover of a 4-in (102-mm) outlet box. With the threaded type the
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10.95
reflectors can be taken down for cleaning, and different reflectors inserted in the same
hood, depending on the distribution curve of light desired. The snap-on type is designed so
that is can be fastened on pendant sockets. The reflector holder snaps on the reflector, and
then the whole assembly screws onto the threads on the outside of an ordinary brass socket.
The vaportight type (Fig. 10.77) is for interior use in wet atmospheres. It requires a cast outlet box with a threaded opening. The reflector is bolted to a ring which threads on the outside of the box opening. A threaded glass globe screws into the inside of the box opening
against a gasket, which seals the box against entrance of moisture. A metal guard is used
for low mounting heights or other locations where it is necessary to protect the globe from
mechanical injury. The guard screws on the outside of the box opening.
FIGURE 10.77
Vaportight units. [Miller Lighting, Hubbell Lighting Division]
These enameled-steel–reflector assemblies are all available in several shapes for specific purposes as shown in Figs. 10.78 and 10.79. The flat cone (Fig. 10.78, I) and the shallow bowl (Fig. 10.78, II) are used for yard and aisle lighting for wide distribution of light
when the quality of the light is unimportant and glare from the partially exposed lamp is not
objectionable. The RLM dome (Fig. 10.78, III) is a standard dome reflector which must
comply with standard specifications of the Reflector and Lamp Manufacturers as regards
contour and quality of the porcelain reflecting surface. This type of reflector is commonly
used for general interior industrial lighting. The deep-bowl type (Fig. 10.78, IV) is used
frequently when units must be hung very low, as over workbenches. Angle reflectors
(Fig. 10.79) are used in industrial lighting to supplement overhead units in very high interiors and for special types of service which require very good illumination on vertical
planes. They are used also for the lighting of billboards and painted signs.
Specifically designed deep-bowl units also are available for high-bay mounting.
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10.96
DIVISION TEN
FIGURE 10.78
curves.
Contour outlines of typical enameled-steel reflectors with their characteristic distribution
FIGURE 10.79
Elliptical-angle steel reflector. [Benjamin Division, Thomas Industries, Inc.]
The use of silvered-bowl lamps in steel reflectors will provide well-diffused illumination.
Glass covers are available for enclosing the bottom of steel reflectors to make them
dusttight.
FIGURE 10.80
Glassteel diffuser.
176. The Glassteel diffuser luminaire for
incandescent light is a combination glass-andsteel direct-lighting unit which is employed for
high-quality industrial lighting. It consists of a completely enclosing opal-glass globe (Fig. 10.80)
mounted inside a dome-shaped, porcelain-enamel
reflector. The porcelain reflector has the same general construction as the standard RLM dome reflector. Small openings in the top of the dome allow a
small portion of the light to be directed to the ceiling.
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10.97
This illumination of the ceiling produces natural and cheerful working conditions,
whereas with the RLM dome reflectors the ceiling is left in darkness. The enclosing globe
of the Glassteel diffuser shields the lamp from view and diffuses the light, reducing the
glare effect. The Glassteel diffuser is made in all the types of assemblies explained above
under the discussion of enameled-steel luminaires.
177. Aluminum luminaires for incandescent lamps are chiefly of the high-bay
type (Fig. 10.81). They provide more accurate control of light than is obtainable with the
enameled-steel reflectors and are recommended when the mounting height is high compared with the width of the area to be lighted. A concentrating type is used when the units
are sufficiently high so that it is best to locate them closer together than the mounting height
and for high-mounted units in narrow interiors. A spread type gives better illumination on
vertical surfaces and can be used when the spacing is up to 11/2 times the mounting height.
These luminaires are made in the one-piece and turn-lock types as described in Sec. 175.
Steel-clad units, which consist of an Alzak aluminum reflector protected by a porcelainenamel steel housing, are available for severe service conditions. These units may be provided with glass covers for protection against moisture and noncombustible dust.
FIGURE 10.81 Aluminum high-bay luminaires. [Miller Lighting, Hubbell
Lighting Division]
178. Prismatic-glass luminaires for industrial use with incandescent and HID
lamps are available in low-bay (Fig. 10.82, I, II, and IV) and high-bay (Fig. 10.82, III)
types. The basic unit is provided with an open-bottom prismatic-glass reflector which produces semidirect illumination. When upward light is not required but protection against
moisture (condensate, leakage, etc.) from the ceiling is desirable, an aluminum cover can
be used over the prismatic reflector without materially affecting the downward distribution
of light. Guards of either wire- or louver-type construction are available for protection of
the lamp. These units, in addition to their industrial applications, are widely used in certain
commercial types of buildings, such as gymnasiums and supermarkets.
Another prismatic-glass luminaire for industrial use with incandescent lamps is an allpurpose vaportight and dusttight unit. This luminaire consists of a prismatic-glass reflectorrefractor and a cast-metal filter with stainless-steel supporting bails assembled to normally
closed-type cam latches. This unit is shown in Fig. 10.82, II. It is used in chemical, petroleum, ordnance, generating-station, textile, woodworking, food-processing, and similar
industries.
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10.98
DIVISION TEN
FIGURE 10.82 Industrial-type prismatic-glass HID luminaires. [Manville Special Products Group,
Holophane Division]
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ELECTRIC LIGHTING
10.99
179. Luminaires for high-intensity–discharge lamps are generally intended for
high-bay mounting in industrial interiors. Luminaires are available in enameled steel,
Alzak aluminum, and prismatic-glass types. The metal units are of the same general type
of construction as similar luminaires used for lighting with incandescent lamps. Refer to
Secs. 175 and 177.
Prismatic-glass units are available for both high-bay and low-bay mounting (refer to
Fig. 10.82). Both the high-bay and the low-bay units consist of a prismatic-glass reflector
with the outside of the reflector protected by a sealed and permanently spun-on metal cover.
Other high-bay luminaires utilize reflectors with a coated-glass surface for high efficiency and easy maintenance. Enclosed high-bay fixtures are also available with internal
filter systems which greatly reduce light-output depreciation due to dirt. Low-bay units are
available with acrylic and polycarbonate plastic refractors. (See Fig. 10.83).
FIGURE 10.83
HID industrial luminaires. [GE Lighting Systems]
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ELECTRIC LIGHTING
10.100
DIVISION TEN
180. Industrial luminaries for fluorescent lamps generally employ porcelainenamel steel reflectors. They provide direct illumination. Both open and enclosed units are
available for two- to four-lamp assemblies. The open units may be of the open- or closedend type of construction. The tops of the reflectors may be solid or be provided with apertures (refer to Figs. 10.84, 10.85, and 10.86.) These open units may have a plain reflector,
or the reflector may be fitted with a longitudinal shield or with louvers (refer to Fig. 10.87).
The shield is positioned between the lamps and provides a crosswise shielding angle of
approximately 27 from the horizontal. Closed units are provided with glass or plastic covers across the bottom of the luminaire. Closed units with sealed covers are available for hazardous locations (see Fig. 10.88).
Different mounting methods are shown in Fig. 10.89.
FIGURE 10.84 Partially open-end type of steel fluorescent luminaire. [Miller
Lighting, Hubbell Lighting Division]
FIGURE 10.85 Construction of an open-type fluorescent luminaire, showing
longitudinal shield. [Miller Lighting, Hubbell Lighting Division]
FIGURE 10.86
cent luminaire.
Closed-end type of steel fluores-
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.101
FIGURE 10.87 Louver for use with an open-type fluorescent luminaire. [Miller
Lighting, Hubbell Lighting Division]
FIGURE 10.88 Closed-type fluorescent luminaire for hazardous locations.
[Benjamin Division, Thomas Industries, Inc.]
FIGURE 10.89 Methods of suspension for industrial fluorescent
luminaires. [Miller Lighting, Hubbell Lighting Division]
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ELECTRIC LIGHTING
10.102
DIVISION TEN
181. The ballast for fluorescent lamps is mounted in the supporting channel or
base of the luminaire. The construction to accommodate the ballast for one type of luminaire is shown in Fig. 10.90.
FIGURE 10.90
Construction of a fluorescent luminaire.
182. Fluorescent luminaires for commercial lighting are made in a great
variety of types. They can be obtained to produce illumination of any one of the different systems of illumination listed in Sec. 156, item 1. All the materials listed in Sec. 156,
item 4, are employed for the reflection and diffusion of the light in fluorescent luminaries of the different constructions available. Probably the best method of obtaining an
appreciation of the various types available is through a study of the latest catalogs of fixture
manufacturers.
Commercial fluorescent luminaires may be classified as follows:
1. Large-area ceiling units
2. Troffers
3. Conventional suspended or surface units
Large-area ceiling units (refer to Figs. 10.91, 10.92, and 10.93) are available in 2- by 2-,
2- by 4-, and 4- by 4-ft (0.6- by 0.6-, 0.6- by 1.2-, and 1.2- by 1.1-m) panels which can be
mounted to achieve almost any geometrical design. The luminous surface of the panels may
be made of glass or plastic. Units are available for surface or recess mounting.
Translucent wall-to-wall lighting (Fig. 10.94) is illumination by means of one large
luminous area. It does not employ luminaires unless the whole luminous ceiling is considered one large luminaire. The diffusing panels for wall-to-wall lighting may be of plastic
or louver construction.
Troffers are fluorescent luminaires which are mounted in recesses in the ceiling so that
the surface of the unit is practically flush with the ceiling. A typical troffer luminaire is
shown in Fig. 10.95, and the method of installing troffers in a suspended plaster ceiling in
Fig. 10.96. Troffers are available for installation in almost any type of ceiling. Troffers
(Fig. 10.97) may be of the open type, louvered, or covered with a glass, prismatic-glass, or
plastic cover.
Conventional suspended or surface luminaires (Figs. 10.98 and 10.99) are available in
units for producing illumination of any one of the systems.
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.103
FIGURE 10.91 Luminaires utilizing mercury, metal halide, or high-pressure sodium lamps. [Manville
Special Products Group, Holophane Division]
FIGURE 10.92
Illumination with large-area fluorescent ceiling units.
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ELECTRIC LIGHTING
10.104
DIVISION TEN
FIGURE 10.93 Large-area surface-mounted fluorescent luminaire. [Day-Brite Lighting Division,
Emerson Electric Co.]
FIGURE 10.94
Wall-to-wall fluorescent lighting.
FIGURE 10.95 Troffer fluorescent luminaire. [Miller Lighting, Hubbell
Lighting Division]
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ELECTRIC LIGHTING
FIGURE 10.96
Installation of flanged troffers in a suspended plaster ceiling.
FIGURE 10.97
Covers for troffer luminaires. [Benjamin Division, Thomas Industries, Inc.]
FIGURE 10.98 Direct-indirect fluorescent luminaire. [Day-Brite Lighting Division,
Emerson Electric Co.]
10.105
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ELECTRIC LIGHTING
10.106
FIGURE 10.99
DIVISION TEN
Semi-indirect fluorescent luminaire. [Miller Lighting, Hubbell Lighting Division]
183. The size of luminaire for an incandescent lamp should be such that its
wattage rating will correspond to the wattage rating of the lamp to be used with it. This
is necessary for the proper distribution of light, for adequate dissipation of the heat produced by the lamp, and for prevention of excessive brightness of the unit. An exception
is the use of a smaller-size lamp if an adapter is employed in the socket to bring the lamp
bowl into the proper position in the luminaire. When replacing lamps, always use the
same size that was used previously unless careful investigation has shown a different size
to be satisfactory.
PRINCIPLES OF LIGHTING-INSTALLATION DESIGN
184. The general purpose of artificial lighting is to enable things to be seen
readily. Since things are seen by the light which is reflcted from them (see “Brightness,”
Sec. 39) into the eye, in an effective lighting installation it is necessary that the number
and arranagement of lighting units render most easily seen those things which it is
desired to see. To accomplish this, recognition must be made of the effect of light on the
human eye.
185. Physiological features of artificial lighting. To appreciate properly the
principles of scientific lighting, it is necessary
to understand the mechanism of the eye.
Figure 10.100 (from Primer of Illumination,
copyright by the Illuminating Engineering
Society) shows the parts of the eye as they
would appear if it were cut through from back
FIGURE 10.100 Essential parts of the eye
to front vertically. In the process of seeing, the
shown in section.
light passes through the cornea, pupil, and
lens of the eye to the retina, just as in a camera light passes through the lens to the sensitized film. The picture is formed on the retina,
which is a layer made up of the ends of nerve fibers that gather into the optic nerve and go
directly to the brain.
186. The optic nerve sends the picture to the brain. The lens of the eye, unlike
that of the camera, automatically changes in thickness to focus or make a clear image on
the retina for seeing at different distances. This focusing action is called the accommodation of the eye, and when the light is dim or bad, the focusing muscle vainly hunts for some
focus which may make objects look clear and gets tired in trying to do it. The muscles
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ELECTRIC LIGHTING
10.107
which move the eye about also get tired in the same way, and the result is eyestrain, which
stirs up pain and headache just as any other overtired muscles of the body may set up
an ache.
187. The iris, which gives the eye its
color, serves to regulate the amount of light
that reaches the eye. In very dim light it
opens out, making the pupil big, as shown in
Fig. 10.101), and in very bright light it shuts
up as shown and thus keeps out a flood of
brilliant light which might hurt the retina.
The protective action of the pupil is fairly
good but by no means complete, for it seldom becomes smaller than shown in the
illustration, however bright the light. From a
study of Fig. 10.101 we may deduce:
FIGURE 10.101 Expansion and contraction of
the pupil of the eye.
1. When trying to see any object, do not allow a light to shine into the eyes, and do not face
a brightly lighted area. In addition to tiring the retina, the superfluous light causes the
pupil to contract, so that less light from the lighted object reaches the retina. An object
which would seem well lighted in a room with dark walls and with no light shining in
the eyes will appear poorly lighted in a bright room with light walls or when a light is
shining in the eyes, simply because the pupil is smaller. This also explains why a higher
light intensity is necessary in the daytime than at night. It is generally easier to read with
the same light source in a room having dark walls than if the walls are light in color,
though the total illumination on the page will probably be less. Reflected light from
glossy paper produces the same effect as light surroundings. The effect produced by a
light shining directly into the eyes is termed glare (see Sec. 38).
2. A fluctuating light causes the pupil to be constantly changing. This is very tiring to the
muscles controlling the iris and if long continued may cause a permanent injury.
3. The lens of the eye is not corrected, as is a photographic lens, for color variations. It cannot focus sharply red and blue light from the same object simultaneously, although ordinarily this is not noticed. As white light is composed of all colors, it follows that we can
see more clearly (i.e., objects appear sharper and more distinct) by a monochromatic
light (light of only one color) than even by daylight. The light from mercury-vapor
lamps closely approximates this condition.
4. Illumination should be uniform; otherwise the eye, in continually attempting to adapt
itself to the unequal conditions, becomes tired as with a fluctuating light.
Correct lighting enables one to see clearly with minimum tiring of the eyes. To secure
this, all the above conditions must be satisfied.
188. The requirements of a satisfactory lighting installation (Ward Harrison,
Electric Lighting) are (1) sufficient light of unvarying intensity on all principal surfaces,
whether horizontal, vertical, or oblique planes; (2) a comparable intensity of light on adjacent areas and on the walls; (3) light of a color and spectral character suited to the purpose
for which it is employed; (4) freedom from glare and from glaring reflections; (5) light so
directed and diffused as to prevent objectionable shadows or contrasts of intensity; (6) a
lighting effect appropriate for the location and lighting units which are in harmony with
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ELECTRIC LIGHTING
10.108
DIVISION TEN
their surroundings, whether lighted or unlighted; and (7) a system which is simple, reliable,
easy to maintain, and in initial and operating cost not out of proportion to the results
attained. Neglect of any of these may result in an unsatisfactory installation.
189. Intensity of illumination. Although the eye is capable of adjusting itself to perceive objects over a wide range of intensities, the speed of this perception and the ability to
distinguish fineness of detail are improved as the intensity increases, until the intensity
becomes so great that a blinding effect is produced. An intensity of illumination that will
be so high as to produce a blinding effect is, however, far above the range of intensities utilized in artificial illumination. The effect of the intensity of illumination upon the length of
time required for the perception of objects is shown in Fig. 10.102A. The effect of the intensity of illumination upon the length of time required for the discrimination of detail is
shown in Fig. 10.102B. From a study of the curve of Fig. 10.107A it is seen that the speed
of perception increases approximately proportionally to the intensity of illumination, until
an illuminatin of 5 fc (53.8 lx) is reached. Above this point the increase in speed of perception for a given increase in intensity gradually decreases. From these facts it was at
one time erroneously considered that intensities of illumination above 5 fc were of little
practical value in making things more clearly seen. That this is not true has been definitely
proved not only by laboratory tests but also by practical tests in actual working areas. High
levels of illumination have been found to result in an actual saving in dollars and cents
owing to the increased production and decrease in spoilage produced by their use.
Recommended values of intensities are given in Table 220.
FIGURE 10.102A Effect of intensity of illumination upon time for perception. [General Electric
Co.]
FIGURE 10.102B Effect of intensity of illumination upon time required for discrimination of detail.
[General Electric Co.]
190. Blink test. To have some definite and scientific way of measuring eyestrain and
fatigue, the General Electric Co. devised the blink test. In this test the number of blinks per
minute which the eye makes involuntarily are counted. This is done when the eyes are in a
rested condition and then again after an hour of work at the various usual tasks of the individual under different levels of illumination. The rate of increase in blinking is taken as a
measure of eye and nerve fatigue. The rate of blinking always increases somewhat with
working or reading, but the higher the illumination intensity, up to at least 75 or 100 fc
(807.3 or 1076.4 lx), the lower the rate of blinking, especially when attention to detail is
required.
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.109
191. Elimination of glare. In designing a lighting installation the greatest care
should be exercised to avoid the presence of any one of the three types of glare described
in Sec. 38. So that a lighting unit in the central portion of the visual field may not produce
glare, its brightness should not exceed from 2 to 3 cd/in2 of apparent area. The maximum
permissible brightness is, of course, influenced by the darkness of the surroundings.
No less important than the elimination of direct glare is the avoidance of reflected glare
of specular reflection. Its effects are often more harmful than those due to direct glare. The
use of highly polished furniture, plate-glass desktops, and glossy finishes on walls should
be avoided. A large expanse of too-light-finished wall surface will cause harmful glare in
offices, schoolrooms, and other locations where the occupants of the room must sit facing
the wall for long periods of time. Although it is always desirable to have walls finished in
light colors such as cream or buff in order to utilize as effectively as possible the light emitted by the source, the reflection factor of the lower walls should not be so high as to cause
eye fatigue. For rooms in which occupants must face the walls for long periods, the reflection factor of the wall below eye level should not exceed 50 percent.
192. Production of shadows. The character of the shadow cast by an object
depends upon the uniformity of the illumination in the area and upon the direction of the
light falling upon the object. If the light falling upon an object is coming from one direction only, a sharp, dense shadow will be cast. As the number of directions in which light is
impinging upon an object is increased, the sharpness and denseness of the shadow cast will
be reduced. A shadow will still be cast even if the object is illuminated from all directions
unless the intensity of the illumination is the same in all directions. Therefore, to eliminate
shadows completely the illumination must be uniform and completely diffused; that is, illumination of any point will be produced by light from all directions. The less uniform the
illumination is or the fewer the directions of light falling upon an object, the more dense
and sharp will be the shadows cast.
The desirability of shadows in an illuminated area depends upon the nature of the installation. In no installation is it desirable to have complete uniformity of illumination, that is,
illumination with no shadows or contrast in the intensity of illumination. Such illumination
would produce a cold and flat effect tiresome to the eye. Nor could the shape and contour
of objects be discerned. On the other hand, it is equally bad to have illumination which
results in very dark, dense shadows and excessive contrasts in the intensity of illumination
of different areas. Such illumination would be very hard on the eyes, owing to the continual change in the size of the pupil as the field of vision varies. When shadows are too dark,
an object cannot be distinguished from its shadow; the shape of object is discernible from
its shadow and without great contrast in intensity of illumination.
Shadows of the proper quality are of great value in observing objects in their three
dimensions, in determining the shape of an object, and in determining irregularities in surfaces. They are of no value in the observation of plane surfaces. Shadows should never be
dark and dense. If shadows are essential, they should be soft and luminous so that the object
is clearly discernible from its shadow and so that there is no great marked contrast in intensity of illumination.
193. Uniformity of illumination is usually expressed as a maximum deviation from
the average or mean intensity of illumination. It is not necessary to have the illumination of
an area exactly uniform in order that the contrasts in the illumination of different portions will
be unobservable by the eye or that the shadows will be too dense or sharp. The degree of uniformity of illumination obtained depends on the ratio of the spacing distance of the lighting
units to their mounting height that should not be exceeded if satisfactory uniformity of
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ELECTRIC LIGHTING
10.110
DIVISION TEN
FIGURE 10.103 Effect of spacing of outlets on
uniformity of illumination.
illumination is to be obtained. The effect of
the spacing of the units upon the uniformity of
illumination is illustrated in Fig. 10.103.
Although this maximum spacing distance
varies somewhat for reflectors distributing
differently the light emitted by them, it is a
good general rule to make the spacing distance equal to the mounting height. A greater
spacing distance is likely to result in sharp
and too dense shadows. One need not hesitate
to use a closer spacing distance than that
equal to the mounting height if desired, since
the closer the spacing, the more uniform will
be the illumination of the area. For the average installation it is best to keep the spacing
distance of the units within the values recommended for specific luminaires. If the ceiling
is unusually high, closer spacing distances
may be advisable to reduce the density of the
shadows. In the illumination of certain areas
such as storage spaces, it is permissible to
space the units slightly farther apart.
194. Methods of illumination. With respect to the arrangement of the light sources
the methods of illumination may be divided into four classes as follows:
1.
2.
3.
4.
Localized
General
Group or localized general
Combination of general and localized
In the localized method an individual lighting unit of small wattage is supplied for each
worker, machine, or workbench; the units are supported at a low level to bring the light
close to the work. There is no attempt to produce uniform illumination over the total area.
With the general illumination method the lighting units are supported fairly close to the
ceiling or at least at a considerable distance above the working plane. They are spaced uniformly throughout the area without special regard to the location of machinery, furniture,
and the like, and at such a distance from one another as to give nearly uniform illumination.
The group method is somewhat of a compromise between the localized and general
methods. The lighting units are mounted close to the ceiling or at a considerable distance
above the working plane. The units are not spaced uniformly but are located with respect
to the machinery, position of operators, etc., so as to give sufficient illumination for work
at each machine. The illumination of the area is not uniform.
In the combination of general and localized methods uniform illumination is supplied
over the complete area by means of units located according to the general method. This illumination is supplemented with local lights for certain operations that require a higher intensity than that required for the main area.
195. Comparison of methods of illumination. The localized arrangement of
lighting units in industrial and most commercial applications should be a thing of the past
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ELECTRIC LIGHTING
10.111
and should never be tolerated. It produces very dense shadows and such low intensities in
the general area that it is likely to cause very serious accidents. Such a method will prove
to be very harmful to the occupants of the room, owing to direct glare from the low-hung
lamps, and may so blind the operators of machines that they can be severely injured.
For the great majority of installations the general method of arranging light sources is
the most satisfactory. It is the method most commonly employed. For some classes of work
which require a very high intensity of illumination at the working point, it would not be
economical to light the whole area to this high intensity. These conditions can be satisfactorily met by means of the combination of the general and localized methods, provided the
local lamps are well shielded to prevent the possibility of glare. With the combination
method the ratio of local to general illumination intensity should not be greater than 10:1.
In other words, if some operations require 75 fc (807.3 lx), the general illumination should
be not less than 71/2 fc (80.7 lx).
In places where there are machines with large overhanging parts and in rooms with high
obstructions, the group method will direct the light upon the working parts better than the
general arrangement. The group method is frequently a good arrangement for rooms containing a number of similar machines arranged in rows.
196. Effect of proportions of a room. Of the light which strikes the walls of a room,
only part is reflected back into the room to become useful upon the working plane.
Consequently, the greater the proportion of the total light that is directed to the walls, the lower
the intensity of illumination on the working plane, or, stated in another way, the greater the
proportion of the total light that is directed to the walls, the larger must the lamps be to produce
a given intensity on the working plane. The proportion of the light that strikes the walls
depends upon the size of the room and the height at which the units are mounted. In a large
room the ratio between the wall area and the floor area is less than for a small room. Thus, for
the same mounting height a smaller proportion of the total light will strike the walls than in a
small room. In large rooms, therefore, less light is absorbed by the walls than in small rooms.
In a room of given dimensions, if the mounting height of the units is increased, more light
will fall upon the walls. One should be careful not to get the impression that it is best to mount
the units as low as possible. Although less light is absorbed by the walls with low-hung units,
there are other more important factors that are affected by the mounting height. As the mounting height of the units is reduced, the spacing between them must also be reduced so that uniform illumination is produced and the shadows are not too dense. The cost of installing a large
number of small units is greater than that of installing a smaller number of larger units. Also,
the larger-size lamps are much more efficient with respect to the number of lumens produced
per watt. As a result, the saving from the use of large units mounted high more than offsets
the increased absorption of light by the walls. For practically all installations it is best to
mount the units as high as possible. There is less probability of glare with high-mounted units
than with low-hung ones, since the units are not so likely to be in the field of view.
197. Room cavity ratios. A room cavity ratio is used as the measure of the effect of
room porportions upon the useful utilization of the light given out by the luminaire. Values
of room cavity ratios are given in Table 212. The room cavity ratio serves as a reference
index for use with Tables 217, 218, and 219 in determining the coefficient of utilization.
198. Effect of character of finish of walls. Of the light that falls upon the walls or
ceiling of a room, the percentage that is reflected back into the room depends upon the color of the
wall and ceilings and the type of paint employed. The lighter the color, the greater the coefficient
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ELECTRIC LIGHTING
10.112
DIVISION TEN
of reflection. The reflection factor of two freshly painted walls of practically the same color may
differ, however, by several percent, depending upon the grade of paint employed. The reflection factor of a surface decreases as time elapses after painting. The amount of this depreciation in reflecting power varies widely with different grades of paint. It is important to have
the walls and ceiling light in color and to employ a good grade of paint which will have a high
initial reflection factor that does not depreciate an excessive amount with age. The walls,
however, should not be made so bright as to be a source of glare (see Sec. 191).
199. Location of lighting equipment. The lighting units for general illumination
should be located symmetrically throughout the area to be illuminated. When the room is
divided into bays by means of columns, roof trusses, or girders or when the ceiling is
divided into panels, the units should be arranged symmetrically, for the sake of appearance, with respect to such architectural divisions, provided the arrangement will not interfere with the uniformity of illumination. Fluorescent luminaires generally are arranged in
rows or in some other symmetrical pattern which will fit in with the architectural arrangement of the area and the utilization of the space. Incandescent and mercury-vapor units
generally are arranged in the form of squares or rectangles. Typical layouts are shown in
Fig. 10.104.
It is important that the units be placed at the centers of squares and not at the corners.
Figure 10.105 shows a method of locating outlets which is undesirable because it gives a
very low intensity of illumination near the walls compared with that at the center of the
room. Figure 10.106 shows the correct method of locating outlets in the centers of the
squares. In certain cases, notably in office lighting and in rooms with benches located along
the walls, it may, to minimize shadows, be desirable to place the outer rows of outlets somewhat nearer the sidewalls of the room than they would be if symmetrically arranged as
shown in Fig. 10.106.
In laying out a lighting installation the maximum permissible spacing distance for the
production of uniform illumination and satisfactory density of shadows should be determined first. The maximum permissible spacing for direct, semidirect, or general diffusing
luminaires depends upon the candlepower-distribution characteristics of the luminaire.
After the maximum spacing has been determined, locate the units on a plan of the area
so that they will be positioned symmetrically with respect to architectural conditions and at
the same time will not exceed the maximum permissible spacing distance.
When the outlets are located above traveling cranes, the staggered system (Fig. 10.104e)
is preferable so that as the crane moves along, it cuts off the light from only one unit at a
time. If it is not desired to use the staggered system, additional lighting outlets, with special
shock-absorbing sockets, should be located on the underside of the crane truss so that as the
crane moves along, the light from those units replaces the light from the regular outlets
which are cut off by the crane.
In buildings of mill-type construction the units are usually supported on the lower chord
of the roof truss or suspended from the roof purlins. When the units are mounted on the
lower chord of the roof truss, the illumination near the walls at each end of the building is
low. When work must be carried on in these areas, it is better to support the units from the
purlins or to locate a row of angle units along each end wall.
High mounting is desirable because then the lamps are out of the way of cranes and
are less apt to be broken, glare is reduced to a minimum, and in the case of a light ceiling there is more reflection and better diffusion of light. The lamps should be lowered in
locations where there is horizontal overhead belting, to the level of the bottom of the belting; otherwise, a portion of the light is ineffective. It may be necessary, for the same reason, to install two or three units in an area where conditions would otherwise warrant
only one unit.
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.113
FIGURE 10.104 Layouts of lighting units for symmetrical spacing. [General Electric Co.]
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ELECTRIC LIGHTING
10.114
DIVISION TEN
FIGURE 10.105 Incorrect arrangement
of lighting units.
FIGURE 10.106 Correct arrangement
of lighting units.
200. Reflection factor is the percentage of light reflected from a surface, such as a
wall or ceiling, to the total light falling on the surface. The difference between the reflection factor and 100 percent represents the percentage of light which is absorbed by the
surface and lost. Reflection factors for some of the common colors are given in Table 215.
The reflection factor varies with the roughness of the surface as well as with the darkness
of the color.
201. The coefficient of utilization is the overall efficiency of the lighting installation: the ratio of the useful lumens which get down to the working plane to the total lumens
generated by the lamp. Tables 217, 218, and 219 give values for the coefficient of utilization for different types of luminaires, subdivided according to room cavity ratios and reflection factors for walls and for the ceiling. For more complete data refer to the IES Lighting
Handbook.
202. Maintenance of lighting equipment. The intensity of illumination produced
by a lighting installation will be somewhat less after the system has been in use for some
time than it was when the system was first installed. This depreciation in the lighting system with time is due to the decrease in efficiency of the lamp in use and to the decrease in
reflecting efficiency of the reflecting equipment, walls, and ceiling, which is the result of
the natural deterioration of the surface with age and of the collection of dust and dirt.
In the design of lighting installations, a maintenance factor is used to take into account
this depreciation. It has values less than unity, so that when the initial illumination is multiplied by the maintenance factor, the actual illumination after a period of several months’
use will be obtained.
The amount of depreciation will vary from 25 to 45 percent, corresponding to a maintenance factor of 0.75 to 0.55, depending upon the type and material of the reflecting equipment, the system of illumination employed, the local conditions of dust and dirt, and the
frequency of cleaning of equipment and repainting of walls. All lighting units should be
adequately cleaned at regular intervals to prevent a waste of energy and low intensity of
illumination. The frequency of the cleaning periods depends upon the degree of prevalence
of dust and dirt and upon the type of luminaire.
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ELECTRIC LIGHTING
10.115
ELECTRIC LIGHTING
203. Four principal methods are used in calculating illumination:
1.
2.
3.
4.
Point-by-point method
Lumen-per-foot method
Zonal-cavity method (general lighting)
Beam-lumens method (floodlighting)
204. The point-by-point method is based on the inverse-square law that the intensity of light flux varies inversely as the square of the distance from the light source to the
point of measurement (see Sec. 26 and Fig. 10.107). The illumination on any plane perpendicular to the light rays is given by the following formula:
Footcandles (on perpendicular plane) cd
D2
(6)
where cd the candlepower of the light source in the direction in which the distance D
is taken and D the perpendicular distance from the light source to the illuminated plane
in feet.
Since the illumination of the horizontal plane is the value usually desired, the formula
must be multiplied by the ratio H/D (see Fig. 10.107), or
Footcandles (on horizontal plane) cd H
D3
(7)
If the illumination on a vertical plane is desired, the basic formula (6) must be multiplied by the ratio X/D (see Fig. 10.112), or
Footcandles (on vertical plane) The illumination at any point is obtained by
adding the footcandles due to each light source
which is sending rays of light to the point.
It is obvious that the point-by-point method
is practical for use only with the direct type of
lighting, for with any other system of illumination the number of light sources which would
have to be considered would make the calculations prohibitively tedious. Even with the
direct system it is usually necessary to calculate the footcandles from several different light
sources. This method is especially applicable
to calculating localized lighting when only a
single light source needs to be considered.
cd X
D3
(8)
FIGURE 10.107 Point-by-point method of
lighting calculations.
205. Lumen-per-foot method (General Electric Co.). The predetermining of lighting levels for supplementary lighting systems in which continuous linear sources are used
can be accomplished from empirical data based on the lumens per foot of the source. These
data are adaptable for relatively short distances between the light source and the work or
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ELECTRIC LIGHTING
10.116
DIVISION TEN
display to which the inverse-square law obviously does not apply. The lumen-per-foot
method employs the following formulas:
Where the lamp and reflector have been selected,
Footcandles K lumens per foot of source
(9)
Where a footcandle level is desired,
Necessary lumens per foot footcandles desired
K
(10)
In formulas (9) and (10) the constant K refers, respectively, to either one of two constants
KH and KV as given in Tables 206, 207, 208, and 209 for horizontal and vertical illumination.
Two types of luminaires are specified: broad distribution as from a unit with a matfinish reflector and narrow distribution as from a polished metal reflector. The beam in both
cases is presumed to be aimed at a plane 4 ft (1.2 m) from the source through point A.
The importance of the reflector is evident from a comparison of Tables 208 and 209.
The average K value at 4 ft in 208 is 0.009; in 209, 0.021. This difference is 133 percent.
The actual values from which the tables were compiled are readings taken at the midpoint of luminaires 12 ft (3.7 m) in length. For conventional lighting systems, the footcandle levels would normally drop at the end of rows unless additional lamps or lamps of
higher output were provided.
206. Horizontal Illumination
(Horizontal fc KH lamp lumens per foot)
(Broad distribution—white-enamel reflector)
Distance between
lamp center and plane
of measurement, ft
1
2
3
4
KH values (distance from centerline of unit), ft
0
1
2
3
0.438
0.223
0.145
0.106
0.127
0.150
0.120
0.095
0.008
0.061
0.077
0.072
0.001
0.017
0.041
0.048
207. Horizontal Illumination
(Horizontal fc KH lamp lumens per foot)
(Narrow distribution—polished aluminum reflector)
Distance between
lamp center and plane
of measurement, ft
1
2
3
4
KH values (distance from centerline of unit), ft
0
1
2
3
0.753
0.330
0.212
0.153
0.079
0.165
0.161
0.131
0.035
0.066
0.086
0.006
0.022
0.038
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ELECTRIC LIGHTING
10.117
ELECTRIC LIGHTING
208. Vertical Illumination
(Vertical fc KH lamp lumens per foot)
(Broad distribution—white-painted cornice; no reflector)
Distance between
lamp center and plane
of measurement, ft
1
2
3
4
Kv values (distance from centerline of unit), in
3
6
9
12
18
0.185
0.011
0.004
0.002
0.159
0.028
0.010
0.005
0.175
0.044
0.017
0.008
0.165
0.057
0.023
0.012
0.129
0.068
0.032
0.018
209. Vertical Illumination
(Vertical fc KV lamp lumens per foot)
(Narrow distribution—polished aluminum reflector)
Distance between
lamp center and plane
of measurement, ft
1
2
3
4
Kv values (distance from centerline of unit), in
3
6
9
12
18
0.121
0.028
0.010
0.006
0.125
0.056
0.028
0.013
0.135
0.077
0.036
0.020
0.096
0.086
0.044
0.031
0.080
0.090
0.059
0.037
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ELECTRIC LIGHTING
10.118
DIVISION TEN
210. Lumens per Foot (Initial Lumens per Nominal Length) for Fluorescent
Lamps (Standard Cool White)a
(General Electric Co.)
General-line lamps
Lamp designation
Lumens per foot
Lumens (initial)
Nominal length, ft
4WT-5
6WT-5
8WT-5
13WT-5
14WT-12
15WT-8
15WT-12
20WT-12
30WT-8
30WT-12
40WT-12
270
393
400
486
520
550
507
600
725
742
762
135
295
400
850
650
825
760
1200
2175
2225
3050
6
9
12
21
15
18
18
24
36
36
48
Slimline lamps
Lamp designation
Lumens per foot
Lumens (initial)
Nominal
length, in
Watts (nominal)
42 T-6
64 T-6
72 T-8
96 T-8
48 T-12
72 T-12
96 T-12
500
525
500
506
600
750
769
1750
2800
3000
4050
2400
4500
6150
42
64
72
96
48
72
96
25.0
40.0
35.0
50.0
40.0
55.0
75.0
48
72
96
60.0
85.0
110.0
High-output rapid-start lamps
48 T-12
72 T-12
96 T-17
1012
1058
1112
4050
6350
8900
a
For lumens per foot of other colors use the following multiplying factors: deluxe cool white, 0.71; deluxe warm
white, 0.71; daylight, 0.93; soft white, 0.68; green, 1.2; gold, 0.6; blue, 0.45; and pink, 0.45.
211. The zonal-cavity method. The lumen method of calculating illumination,
which has been in use for many years, is based on the theory that average illumination is
equal to lumens divided by the work area over which they are distributed. Newer methods
of analysis of lighting distributions, taking into account the concept of interreflection of
light, have led to more accurate coefficient-of-utilization data and have been adopted in the
Illuminating Engineering Society (IES) approved method of lighting calculations called the
zonal-cavity method. This method provides increased flexibility in lighting calculations,
including greater accuracy, but still adheres to the basic concept that footcandles are equal
to light flux over an area (the lumen method).
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.119
FIGURE 10.108 Basic cavity dimensions of space.
The zonal-cavity method assumes that an area to be lighted will be made up of a series
of cavities which have effective reflectances with respect to one another and to the work
plane. Basically, the area is divided into three spaces, or cavities, a ceiling cavity, a room
cavity, and a floor cavity. These are shown graphically in Fig. 10.108.
In using the zonal-cavity method, there are four basic steps to be followed in making a
calculation: (1) determine cavity ratios, (2) determine effective cavity reflectances, (3) select
coefficient of utilization, and (4) compute average footcandle level.
Step 1. Determine Cavity Ratios. Cavity ratios may be determined by calculation,
using formulas (15), (16), and (17) in Sec. 216, which is the basic and most accurate
method; or the values may be found in Table 212 for typical-size cavities which cover
a wide range of room dimensions. For a more complete table of cavity ratios, see the
IES Lighting Handbook.
Step 2. Determine Effective Cavity Reflectances. Table 213 provides a means of converting the combination of actual wall and ceiling or actual wall and floor reflectances
into a single effective ceiling cavity reflectance cc and a single effective floor cavity
reflectance fc. Note that if the luminaire is recessed or surface-mounted or if the floor
is the work plane, the ceiling cavity ratio or floor cavity ratio will be 0, and then the
actual reflectance of the ceiling or floor will also be the effective reflectance. When
using reflectance values of room surfaces, the expected maintained values should be
used for calculation of maintained footcandles, or if initial footcandle values are
desired, the initial reflectance values should be used.
Step 3. Select Coefficient of Utilization (CU). Using the cc, fc, and W (wall
reflectance) determined in step 2 and knowing the room cavity ratio previously calculated in step 1, formula (16), in Sec. 216, refer to the coefficient of utilization in the
CU table for the luminaire under consideration. Tables showing CU values for currently typical, popular types of luminaires are given in Tables 217, 218, and 219. For
more complete data, see the IES Lighting Handbook. Manufacturers of lighting equipment will supply CU data for their own luminaires upon request. Note that since the
CU tables are linear, linear interpolations can be made for exact cavity ratios or
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ELECTRIC LIGHTING
10.120
DIVISION TEN
reflectance combinations. Most CU tables are based on an effective floor cavity
reflectance of 20 percent. Table 214 can be used to revise the CU for other effective
floor cavity reflectances.
In determining the coefficient of utilization for a fluorescent luminaire, it is important that the specific lamp and ballast combination planned for an installation be identified and checked with the fixture manufacturer for any effect on the published CU.
Fluorescent-lamp rated light output is established at 25C (77F). The light output from
all fluorescent lamps varies with temperature (see Sec. 104). Different lamp designs,
such as energy-saving types, do not operate at the same temperature in a specific luminaire, thus will differ in relative light output. Different ballast designs operate at different wattages and vary in losses, both of which affect the temperature in the luminaire
and thus the light output.
Fluorescent-lamp ballasts usually do not operate lamps at rated wattage and light
output. The ratio of lamp light output on a ballast compared with rated light output is
called the ballast factor. Published coefficients of utilization assume rated lamp light
output. Thus the CU for fluorescent luminaires must be multiplied by the ballast factor
for the lamp-ballast combination being used in order to obtain accurate design calculations. The lamp type and ballast type must be identified to establish the specific ballast
factor. Ballast factors can be obtained from ballast manufacturers.
Step 4. Compute Average Footcandle Level. Use the standard lumen method [formula (13) in Sec. 216] to compute the footcandle level that will be obtained. When
maintained illumination levels are to be calculated, the maintenance factor (MF)
should include lamp lumen depreciation (LLD) and luminaire dirt depreciation
(LDD). Light source manufacturers can supply the LLD factor for any type of lamps;
the factor should be based upon the luminaire’s dirt attraction or dirt retention characteristics and the degree of dirtiness of the areas where it is to be used. Procedures
for making these calculations are given in the IES Lighting Handbook.
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ELECTRIC LIGHTING
10.121
ELECTRIC LIGHTING
212. Cavity Ratios
(From IES Lighting Handbook, 4th ed.)
Room dimensions,
feet
Width
Cavity depth
Length
1.0
1.5
2.0
2.5
3.0
4.0
6
8
10
12
10
14
20
1.1
1.0
0.9
1.7
1.5
1.3
2.2
2.0
1.7
2.8
2.5
2.2
3.4
3.0
2.6
4.5
3.9
3.5
6.7
5.9
5.2
9.0
7.8
7.0
11.3
9.7
8.8
11.7
10.5
10
10
14
20
40
1.0
0.9
0.7
0.6
1.5
1.3
1.1
0.9
2.0
1.7
1.5
1.2
2.5
2.1
1.9
1.6
3.0
2.6
2.3
1.9
4.0
3.4
3.0
2.5
6.0
5.1
4.5
3.7
8.0
6.9
6.0
5.0
10.0
8.6
7.5
6.2
12.0
10.4
9.0 12.0
7.5 10.0
12
12
16
36
50
0.8
0.7
0.6
0.5
1.2
1.1
0.8
0.8
1.7
1.5
1.1
1.0
2.1
1.8
1.4
1.3
2.5
2.2
1.7
1.5
3.3
2.9
2.2
2.1
5.0
4.4
3.3
3.1
6.7
5.8
4.4
4.1
8.4
7.2
5.5
5.1
10.0
8.7 11.6
6.6 8.8
6.2 8.2
14
14
20
42
0.7
0.6
0.5
1.1
0.9
0.7
1.4
1.2
1.0
1.8
1.5
1.2
2.1
1.8
1.4
2.9
2.4
1.9
4.3
3.6
2.9
5.7
4.9
3.8
7.1
6.1
4.7
8.5 11.4
7.3 9.8
5.7 7.6
20
20
45
90
0.5
0.4
0.3
0.7
0.5
0.5
1.0
0.7
0.6
1.2
0.9
0.8
1.5
1.1
0.9
2.0
1.4
1.2
3.0
2.2
1.8
4.0
2.9
2.4
5.0
3.6
3.0
6.0
4.3
3.6
8.0
5.8
4.3
30
30
60
90
0.3
0.3
0.2
0.5
0.4
0.3
0.7
0.5
0.4
0.8
0.6
0.6
1.0
0.7
0.7
1.3
1.0
0.9
2.0
1.5
1.3
2.7
2.0
1.8
3.3
2.5
2.2
4.0
3.0
2.7
3.4
4.0
3.6
42
42
90
200
0.2
0.2
0.1
0.4
0.3
0.2
0.5
0.3
0.3
0.6
0.4
0.4
0.7
0.5
0.4
1.0
0.7
0.6
1.4
1.0
0.9
1.9
1.4
1.1
2.4
1.7
1.4
2.8
2.1
1.7
3.8
2.8
2.3
60
60
100
300
0.2
0.1
0.1
0.2
0.2
0.1
0.3
0.3
0.2
0.4
0.3
0.2
0.5
0.4
0.3
0.7
0.5
0.4
1.0
0.8
0.6
1.3
1.1
0.8
1.7
1.3
1.0
2.0
1.6
1.2
2.7
2.1
1.6
100
100
300
0.1
0.1
0.1
0.1
0.2
0.1
0.2
0.2
0.3
0.2
0.4
0.3
0.6
0.4
0.8
0.5
1.0
0.7
1.2
0.8
1.6
1.1
8
16
In making lighting calculations for proposed projects, lighting designers should have all
the facts required for use in their calculations. Included would be the end-use application
of the space; the physical dimensions; the color and reflectance values of the ceiling, walls,
and floor; the layout of furniture or machinery, including colors of the various furnishings,
etc.; and a knowledge of the degree of cleanliness (or dirtiness) of the area which will affect
maintenance of the lighting levels. The degree of accuracy of the lighting calculations is
influenced directly by the degree of accuracy involved in these various factors. The zonalcavity method of making lighting calculations offers a high degree of accuracy in the calculated results, but these results cannot be any more accurate than the data used to make the
calculations, including estimates of maintenance factors.
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ELECTRIC LIGHTING
10.122
DIVISION TEN
213. Percent Effective Ceiling or Floor Cavity Reflectance for Various
Reflectance Combinations
(From IES Lighting Handbook, 4th ed.)
% ceiling or floor reflectance
80
70
50
30
10
Ceiling or
floor
cavity
ratio
70
50
30
70
50
30
70
50
30
50
30
10
50
30
10
0
0.1
0.3
0.5
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
2.8
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.0
80
79
77
75
75
73
71
70
68
67
65
64
63
61
60
59
58
56
54
53
51
50
49
48
80
78
75
73
71
69
66
64
62
60
58
56
54
52
50
48
47
44
42
40
39
37
36
35
80
78
74
70
68
65
61
58
55
53
50
48
45
43
41
39
38
35
33
30
29
27
25
25
70
69
68
66
65
64
63
61
60
59
57
56
55
54
53
52
51
49
48
47
46
45
44
43
70
69
66
64
62
60
58
56
54
52
50
48
46
45
43
42
40
39
37
36
34
33
32
32
70
68
64
61
59
56
53
50
48
45
43
41
39
37
35
33
32
30
28
26
25
24
23
22
50
49
49
48
47
47
46
45
45
44
43
43
42
42
41
41
40
39
39
38
37
37
36
36
50
49
47
46
45
43
42
41
40
39
37
37
36
35
34
33
32
31
30
29
28
27
26
26
50
48
46
44
43
41
39
37
35
33
32
30
29
27
26
25
24
23
21
20
19
19
18
17
30
30
29
28
28
27
27
26
26
25
25
24
24
24
23
23
22
22
21
21
20
20
19
19
30
29
28
27
26
25
24
23
22
21
21
20
19
19
18
18
17
16
15
15
14
14
13
13
30
29
27
25
25
23
22
20
19
18
17
16
15
14
13
13
12
11
10
10
9
8
8
7
10
10
10
11
11
11
11
12
12
12
12
12
13
13
13
13
13
13
13
13
13
14
14
14
10
10
10
10
10
10
9
9
9
9
9
9
9
9
9
9
8
8
8
8
8
8
8
8
10
10
9
9
9
8
8
7
7
7
6
6
6
6
5
5
5
5
5
4
4
4
4
4
wall reflectance
% wall %
reflectance
214. Factors for Effective Floor Cavity Reflectance Other than 20 Percenta
(From IES Lighting Handbook, 4th ed.)
% effective ceiling cavity reflectance, cc
80
70
50
10
% wall reflectance, W
Room cavity ratio
50
30
50
30
50
30
50
30
1
3
5
6
8
10
1.08
1.05
1.04
1.03
1.03
1.02
1.08
1.04
1.03
1.02
1.02
1.01
1.07
1.05
1.03
1.03
1.02
1.02
1.06
1.04
1.02
1.02
1.02
1.01
1.05
1.03
1.02
1.02
1.02
1.02
1.04
1.03
1.02
1.02
1.01
1.01
1.01
1.01
1.01
1.01
1.01
1.01
1.01
1.01
1.01
1.01
1.01
1.01
a
For 30% effective floor cavity reflectance, multiply by appropriate factor above. For 10% effective floor cavity
reflectance, divide by appropriate factor above.
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.123
215. Reflection Factors of Colored Surfaces
Color
Reflection factor, %
Flat white
Ivory
Buff
Yellow
Light tan
Light green
Gray
Blue
Red
Dark brown
75–85
70–75
60–70
55–65
45–55
40–50
30–50
25–35
15–20
10–15
216. Lighting design formulas*
Lumen Method
lumens
area, ft2
(11)
LL CU
area, ft2
(12)
Footcandles Initial fc Maintained fc LL CU MF
area, ft2
MF LLD LDD
where
(13)
(14)
fc footcandles
LL lamp lumens
CU coefficient of utilization
MF maintenance factor
LLD lamp lumen depreciation factor
LDD luminaire dirt depreciation factor
IES Zonal-Cavity Method
Ceiling cavity ratio:
CCR 5hcc(L W)
L W
(15)
RCR 5hrc(L W)
L W
(16)
FCR 5hfc(L W)
L W
(17)
Room cavity ratio:
Floor cavity ratio:
where hcc distance in feet from luminaire to ceiling
hrc distance in feet from luminaire to work plane
hfc distance in feet from work plane to floor
L length of room in feet
W width of room in feet
*From IES Lighting Handbook, 4th ed.
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ELECTRIC LIGHTING
10.124
DIVISION TEN
TABLES FOR INTERIOR ILLUMINATION DESIGN
217. Incandescent Lighting
(Lighting manufacturers’ published reference material)
(Coefficients for utilization for typical luminaires; 0.01)
(Effective floor cavity reflectance 20 percent; fc 0.20)
Effective ceiling cavity reflectance, cc
80
70
50
Wall reflectance, W
Room cavity
ratio, RCR
50
30
50
30
50
30
1
2
5
6
8
10
89
83
79
78
74
71
88
81
77
75
71
69
88
82
79
77
73
71
87
80
76
75
71
69
85
81
78
77
73
71
84
79
75
75
71
69
1
3
5
6
8
10
69
60
52
49
42
36
68
57
48
44
38
32
69
59
51
48
41
36
68
56
47
44
37
32
66
57
50
47
40
35
65
55
47
44
37
32
1
3
5
6
8
10
59
52
47
45
39
35
58
50
44
42
37
32
58
52
46
44
39
35
57
50
44
42
36
32
56
50
46
43
39
34
55
49
43
41
36
32
1
3
5
6
8
10
72
67
63
61
58
56
72
65
60
59
56
54
70
66
62
61
58
56
70
64
60
59
56
54
68
65
61
60
57
55
68
63
59
58
56
53
1
3
5
6
8
10
49
45
42
40
37
35
48
44
40
38
35
33
48
45
41
40
37
35
48
43
40
38
35
33
47
44
41
39
37
34
46
42
39
38
35
33
Typical luminaires,
description
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ELECTRIC LIGHTING
10.125
ELECTRIC LIGHTING
218. High-Intensity–Discharge Lighting
(IES Lighting Handbook, 4th ed., and lighting manufacturers’ published reference material)
(Coefficients for utilization for typical luminaires; 0.01)
(Effective floor cavity reflectance 20 percent; fc 0.20)
Room cavity ratio,
RCR
Typical luminaires,
description
Coefficients of utilization
Effective ceiling
cavity reflectance,
cc Wall
reflectance, w
50
30
50
30
50
30
1
3
5
6
8
10
89
77
65
61
52
42
87
72
60
56
46
36
81
71
62
57
49
39
79
68
58
53
45
35
72
65
57
54
46
37
71
63
54
50
43
37
cc
W
50
30
50
30
50
30
1
3
5
6
8
10
88
77
67
63
56
48
86
73
63
58
51
44
86
76
66
62
54
46
84
72
62
58
51
44
82
73
65
61
54
47
81
70
61
57
50
43
cc
W
50
30
50
30
50
30
1
3
5
6
8
10
103
82
64
54
40
27
100
75
56
49
36
25
99
79
62
53
39
27
96
73
56
48
36
25
93
72
54
47
35
24
91
68
50
43
33
23
1
3
5
6
8
10
77
66
56
52
43
35
76
63
51
47
38
30
73
63
53
49
41
33
71
60
49
45
37
29
68
59
51
47
40
32
67
57
47
43
36
28
80
50
80
10
70
70
50
50
30
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ELECTRIC LIGHTING
10.126
DIVISION TEN
219. Fluorescent Lighting
(IES Lighting Handbook and manufacturers’ catalogs)
(Coefficients of utilization for typical luminaires; 0.01)
(Effective floor cavity reflectance 20 percent; fc 0.20)
Effective ceiling cavity reflectance, cc
80
70
50
Wall reflectance, W
Room cavity
ratio, RCR
50
30
50
30
50
30
1
3
5
6
8
10
73
59
47
43
35
29
70
54
42
38
30
23
70
57
46
42
34
28
68
53
41
37
29
23
66
54
44
40
32
27
64
50
39
35
28
22
1
3
5
6
8
10
69
53
42
38
30
25
66
49
36
31
25
19
67
52
41
37
30
24
65
48
36
31
25
19
65
50
40
36
29
24
63
47
34
30
24
18
1
3
5
6
8
10
71
57
46
42
34
28
69
53
41
36
29
23
69
56
46
41
33
27
67
52
41
36
28
22
67
54
44
40
33
27
65
51
40
36
28
22
1
3
5
6
8
10
58
47
38
34
27
23
56
43
34
30
23
19
57
46
37
34
27
23
55
43
33
30
23
19
55
45
37
33
26
22
53
42
33
29
23
19
1
3
5
6
8
10
70
56
45
41
33
26
68
51
40
35
27
21
67
54
44
39
32
26
65
50
39
34
27
21
63
51
41
37
30
24
61
47
37
33
26
20
1
3
5
6
8
10
86
68
54
49
39
32
83
62
47
42
32
26
82
65
52
47
38
31
79
60
46
40
31
25
75
60
48
43
35
29
72
56
43
38
30
23
Typical luminaires,
description
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ELECTRIC LIGHTING
10.127
ELECTRIC LIGHTING
219. Fluorescent Lighting (Continued)
Effective ceiling cavity reflectance, cc
80
70
50
Wall reflectance, W
Room cavity
ratio, RCR
50
30
50
30
50
30
1
3
5
6
8
10
83
67
53
48
37
29
80
61
47
42
32
24
-
-
74
60
48
43
34
26
72
56
44
39
30
22
1
3
5
6
8
10
66
53
42
38
31
25
64
48
37
33
26
20
-
-
62
50
40
37
30
24
60
46
36
32
25
20
Typical luminaires,
description
220. Levels of illumination. The present Recommended Levels of Illumination,
RP-15, utilizes a sophisticated approach to lighting. It provides flexibility in establishing
lighting levels so that lighting systems can be set to meet specific needs. The procedure
is fully described in the IES Lighting Handbook: Application Volume. Because this
approach is the current state of the art, the prescriptive footcandle tables that appeared at
this location for many editions up through the 11th edition (published in 1987) were subsequently deleted. However, this editor has been made very aware that a great many electricians still value the old tables, to the point of retaining the older editions of this
Handbook.
Therefore, the old tables follow this commentary. The current IES protocol is still the
best way to do these calculations, however, for those who want a prescriptive footcandle
list as a starting point, they are now returned to this volume. Inspection quickly shows that
some of this information, which was last fully updated over twenty years ago, is plainly
dated. Use the list with this caveat firmly in mind.
While for convenience of use this table sometimes lists locations rather than tasks, the
recommended footcandle values have been arrived at for specific visual tasks. The tasks
selected for this purpose have been the more difficult ones which commonly occur in the
various areas. To assure these values at all times, higher initial levels should be provided
as required by maintenance conditions.
When tasks are located near the perimeter of a room, special consideration should be
given to the arrangement of the luminaires to provide the recommended level of illumination on the tasks. The illumination levels shown in the table are intended to be the minimum
on a task irrespective of the plane in which it is located. The commonly used lumen method
of illumination calculation gives results for only a horizontal work plane. The ratio of
vertical to horizontal illumination will generally vary from 1:3 for luminaires having a narrow
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ELECTRIC LIGHTING
10.128
DIVISION TEN
distribution to 1:2 for luminaires of wide distribution. When the levels thus achieved are
inadequate, special luminaire arrangements must be used or supplemental lighting
equipment employed.
Supplementary luminaires may be used in combination with general lighting to achieve
these levels. The general lighting should not be less than 20 fc (21.5 dalx) and should contribute at least one-tenth of the total illumination level.
Area
Footcandles
on tasks*
Area
Footcandles
on tasks*
Interior lighting
Airplane hangars (repair service only)
100
Airplane manufacturing
Stock parts
Production
100
Inspection
200a
Parts manufacturing
Drilling, riveting. screw fastening
70
Spray booths
100
Sheet-aluminum layout and template
work. shaping, smoothing of
small parts for fuselage,
wing sections, cowling, etc.
100
Welding
General illumination
50
Supplementary illumination
1000
Subassembly
Landing gear. fuselage, wing
sections, cowling, other large
units
100
Final assembly
Placing of motors. propellers.
wing sections. landing gear
100
Inspection of assembled plane
and its equipment
100
Machine-tool repairs
100
Armories
Drill
Exhibitions
Art galleries
General
On paintings (supplementary)
On statuary.and other displays
Assembly
Rough, easy seeing
Rough, difficult seeing
20
30
30
30b
100c
30
50
Medium
Fine
Extra fine
Auditoriums
Assembly only
Exhibitions
Social activities
Automobile manufacturing
Frame assembly
Chassis-assembly line
Final assembly, inspection line
Body manufacturing
Parts
Assembly
Finishing, inspecting
100
500
1000
15
30
5
50
100
200a
70
100
200a
Automobile showrooms (see Stores)
Bakeries
Mixing room
Face of shelves
(vertical illumination)
Inside of mixing bowl
(vertical mixers)
Fermentation room
Makeup room
Bread
Sweet yeast-raised products
Proofing room
Oven room
Fillings and other ingredients
Decorating and icing
Mechanical
Hand
Scales and thermometers
Wrapping room
50
30
50
30
30
50
30
30
50
50
100
50
30
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.129
ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Banks
Lobby
General
Writing areas
Tellers’stations
Posting and key punch
50
70
150
150
Barbershops and beauty parlors
100
Bookbinding
Folding, assembling, pasting,
etc.
Cutting, punching, stitching
Embossing, inspection
70
70
200a
Breweries
Brewhouse
Boiling, keg washing
Filling (bottles, cans, kegs)
30
30
50
Candymaking
Box department
50
Chocolate department
Husking, winnowing, fat extraction,
crushing and refining, feeding
50
Bean cleaning, sorting, dipping,
packing, wrapping
50
Milling
00
Cream making (mixing, cooking,
molding)
50
Gumdrops, jellied forms
50
Hand decorating
100
Hard candy
Mixing, cooking, molding
50
Die cutting, sorting
100
Kiss making, wrapping
100
Canning and preserving
Initial grading of raw-material
samples
Tomatoes
Color grading (cutting rooms)
Preparation
Preliminary sorting
Apricots and peaches
Tomatoes
Olives
Cutting, pitting
Final sorting
50
100
200a
50
100
150
100
100
Area
Footcandles
on tasks*
Canning
Continuous-belt canning
Sink canning
Hand packing
Olives
Examination of canned samples
Container handling
Inspection
Can unscramblers
Labeling, cartoning
Central station
Air-conditioning equipment, air
preheater and fan floor,
ash sluicing
Auxiliaries, battery rooms, boiler
feed pumps, tanks, compressors,
gage area
Boiler platforms
Burner platforms
Cable room, circulator or pump bay
Chemical laboratory
Coal conveyor, crusher, feeder, scale
areas, pulverizer, fan area, transfer
tower
Condensers, deaerator floor,
evaporator floor, heater floors
Control rooms
Vertical face of switchboards
Simplex or section of duplex
facing operator
Type A: large centralized
control room 1.7 m (66 in.)
above floor
Type B: ordinary control room
1.7m (66 in.) above floor
Section of duplex facing away
from operator
Benchboards (horizontal level)
Area inside duplex switchboards
Rear of all switchboard panels
(vertical)
Emergency lighting; all areas
Dispatch boards
Horizontal plane (desk level)
Vertical face of board [1.2 m (48 in.)
above floor, facing operator]
System-load dispatch room
Secondary dispatch room
100
100
50
100
200a
200a
70
30
10
20
10
20
10
50
10
10
50
30
30
50
10
10
3
50
50
30
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.130
DIVISION TEN
220. Levels of illumination (Continued)
Area
Hydrogen and carbon dioxide
manifold area
Precipitators
Screenhouse
Soot or slag blower platform
Steam headers and throttles
Switch gear, power
Telephone-equipment room
Tunnels or galleries, piping
Turbine-bay subbasement
Turbine room
Visitors’ gallery
Water-treating area
Footcandles
on tasks*
20
10
20
10
10
20
20
10
20
30
20
20
Chemical works
Hand furnaces, boiling tanks,
stationary dryers, stationary
and gravity crystallizers
30
Mechanical furnaces, generators and
stills, mechanical dryers, evaporators,
filtration, mechanical crystallizers,
bleaching
30
Tanks for cooking, extractors,
percolators, nitrators,
electrolytic cells
30
Churches and synagogues
Altar, ark, reredos
100e
Chaird and chancel
30e
Classrooms
30
Pulpit. rostrum (supplementary
illumination)
50e
Main worship aread
Light and medium interior finishes
15e
For churches with special zeal
30d
Art-glass windows (test
recommended)
Light color
50
Medium color
100
Dark color
500
Especially dense windows
1000
Clay products and cements
Grinding, filter presses. kiln rooms
Molding, pressing, cleaning,
trimming
Enameling
Color and glazing: rough work
Color and glazing: fine work
30
30
100
100
300a
Area
Footcandles
on tasks*
Cleaning and pressing industry
Checking. sorting
Dry and wet cleaning and steaming
Inspection. spotting
Pressing
Machine
Hand
Repair and alteration
Cloth products
Cloth inspection
Cutting
Sewing
Pressing
Club and lodge rooms
Lounge and reading rooms
Auditoriums (see Auditoriums)
Coal tipples and cleaning plants
Breaking, screening. cleaning
Picking
50
50
500a
150
150
200a
2000a
300a
500a
300a
30
10
300a
Control rooms (see Central station)
Courtrooms
Seating area
Court-activity area
Dairy products
Fluid-milk industry
Boiler room
Bottle storage
Bottle sorting
Bottle washers
Can washers
Cooling equipment
Filling: inspection
Gages (on face)
Laboratories
Meter panels (on face)
Pasteurizers
Separators
Storage refrigerator
Tanks, vats
Light interiors
Dark interiors
Thermometer (on face)
Weighing room
Scales
30
70
30
30
50
f
30
30
100
50
100
50
30
30
30
20
100
50
30
70
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.131
ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Dance halls
Depots, terminals, and stations
Waiting room
Ticket offices
General
Ticket rack and counters
Rest rooms, smoking room.
Baggage checking
Concourse
Platforms
Toilets, washrooms
Footcandles
on tasks*
5
30
100
100
30
50
10
20
30
Dispatch boards (see Central station)
Drafting rooms (see Offices)
Electrical-equipment manufacturing
Impregnating
Insulating;:coil winding
Testing
Elevators, freight and passenger
Engraving, wax
Explosives
Hand furnaces, boiling tanks,
stationary dryers, stationary and
gravity cyrstallizers
Mechanical furnace, generators,
stills, mechanical dryers,
evaporators, filtration
mechanical crystallizers
Tanks for cooking, extractors,
percolators, nitrators
Farms: milkhouse
50
100
100
20
200a
30
30
30
10
Fire hall (see Municipal buildings)
Flour mills
Rolling, sifting, purifying
50
Packing
30
Product control
100
Cleaning, screens, man lifts, aisleways
and walkways, bin checking
30
Area
Footcandles
on tasks*
Forge shops
Foundries
Annealing (furnaces)
Cleaning
Core making
Fine
Medium
Grinding, chipping
Inspection
Fine
Medium
Molding
Medium
Large
Pouring
Sorting
Cupola
Shake-out
Garages, automobile and truck
Service garages
Repairs
Active-traffic areas
Parking garages
Entrance
Traffic lanes
Storage
50
30
30
100
50
100a
500a
100
100
50
50
50
20
30
100
20
50
10
5
Gasoline stations (see Service stations)
Glassworks
Mix and furnace rooms, pressing and
lehr, glassblowing machines
Grinding, cutting glass to size,
silvering
Fine grinding, beveling, polishing
Inspection, etching, decorating
50
100
200a
Glove manufacturing
Pressing
Knitting
Sorting
Cutting
Sewing, inspection
300a
100
100
300a
500a
30
Hangars (see Airplane hangars)
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.132
DIVISION TEN
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Hat manufacturing
Dyeing, stiffening, braiding, cleaning,
refining
100
Forming, sizing, pouncing, flanging,
finishing, ironing
200a
Sewing
500a
Homes (see Residences)
Hospitals
Anesthetizing and preparation
room
Autopsy and morgue
Autopsy room
Autopsy table
Morgue, general
Central sterile supply
General
Needle sharpening
Corridor
General
Operating and delivery suites and
laboratories
Cystoscopic room
General
Cystoscopic table
Dental suite
Waiting room
General
Reading
Operatory, general
Instrument cabinet
Dental chair
Laboratory, bench
Recovery room
EKG, BMR, and specimen room
General
Specimen table (supplementary)
Electroencephalographic suite
Office
Workroom
Patients’ room
Emergency room
General
Local
Examination and treatment room
General
Examining table
Exits, at floor
30
100
2500
20
30
150
10
20
100
2500
15
30
70
150
1000
100
5
20
50
100
30
30
100
2000
50
100
5
Area
Footcandles
on tasks*
Eye, ear, nose, and throat suite
Darkroom
10
Eye examination and treatment room 50
Ear, nose, and throat room
50
Flower room
10
Formula room
30
Fracture room
General
50
Fracture table
200
Laboratories
Assay rooms
30
Worktables
50
Close work
100
Linen closet
10
Lobby
30
Lounge rooms
30
Medical-records room
100
Nurseries
General
10
Examination table
70
Playroom, pediatric
30
Nurses’ station
General
20
Desk and charts
50
Medicine-room counter
100
Nurses’ workroom
30
Obstetrical
Cleanup room
30
Scrub-up room
30
Labor room
20
Delivery room: general
100
Delivery table
2500
Pharmacy
General
30
Worktable
100
Active storage
30
Alcohol vault
10
Private rooms and wards
General
10
Reading
30
Psychiatric disturbed patients’ areas
10
Radioisotope facilities
Radiochemical laboratory
30
Uptake measuring room
20
Examination table
50
Retiring room
10
Sewing room
General
20
Work area
100
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.133
ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Solariums
20
Stairways
20
Surgery
Instrument and sterile supply room
30
Cleanup room (instruments)
100
Scrub-up room
30
Operating room, general
100
Operating table
2500
Recovery room
30
Therapy
Physical
20
Occupational
30
Toilets
10
Utility room
20
Waiting room
General
15
Reading
30
X-ray room and facilities
Radiography and fluoroscopy
10
Deep and superficial therapy
10
Darkroom
10
Waiting room, general
15
Waiting room, reading
30
Viewing room
30
Filing room: developed films
30
Hotels
Bathrooms
Mirror
General
Bedrooms
Reading (books, magazines,
newspapers)
Ink writing
Makeup
General
Corridors, elevators, stairs
Entrance foyer
Front office
Linen room
Sewing
General
Lobby
General lighting
Reading and working areas
Marquee
Dark surroundings
Bright surroundings
Ice making: engine and compressor room
30g
10
30
30 h
30i
10
20
30
50
100
20
10
30
30
50
20
Area
Footcandles
on tasks*
Inspection
Ordinary
Difficult
Highly difficult
Very difficult
Most difficult
200a
500a
1000a
Iron and steel manufacturing
Open hearth
Stock yard
Charging floor
Pouring slide
Slag pits
Control platforms
Mold yard
Hot top
Hot-top storage
Checker cellar
Buggy and door repair
Stripping yard
Scrap stock yard
Mixer building
Calcining building
Skull cracker
Rolling mills
Blooming. slabbing. hot-strip.
hot-sheet
Cold-strip. plate
Pipe, rod, tub. wire drawing
Merchant and sheared plate
Tinplate mills
Tinning, galvanizing
Cold-strip rolling
Motor room, machine room
Inspection
Black, plate, bloom, and billet
chipping
Tinplate, other bright surfaces
100
100 j
Jewelry and watch manufacturing
500a
10
20
20
30
5
30
10
10
30
20
10
30
10
10
30
30
50
30
50
50
30
Kitchens (see Residences; Restaurants,
lunchrooms. cafeterias)
Laundries
Washing
Flatwork ironing, weighing. listing,
marking
Machine and press finishing, sorting
Fine hand ironing
30
50
70
100
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.134
DIVISION TEN
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Leather manufacturing
Cleaning, tanning and stretching, vats
Cutting, fleshing, stuffing
Finishing, scarfing
Leatherworking
Pressing. winding, glazing
Grading. matching. cutting. scarfing,
sewing
Library
Reading room
Study and notes
Ordinary reading
Stacks
Book repair and binding
Cataloguing
Card files
Check-in and check-out desks
Locker rooms
30
50
100
Meat packing
Slaughtering
Cleaning, cutting, cooking, grinding,
canning, packing
Municipal buildings: fire and police
Police
Identification records
Jail cells, interrogation rooms
Footcandles
on tasks*
Fire hall
Dormitory
Recreation room
Wagon room
20
30
30
Museums (see Art galleries)
200
300
70
30
30
50
70
70
70
20
Machine shops
Rough bench work and machine work 50
Medium benchwork and machine work,
ordinary automatic machines, rough
grinding, medium buffing and
polishing
100
Fine benchwork and machine work,
fine automatic machines, medium
grinding, fine buffing and polishing 500a
Extra-fine bench work and machine
work, grinding, fine work
1000a
Materials handling
Wrapping, packing, labeling
Picking stock, classifying
Loading, trucking
Inside truck bodies and freight
cars
Area
50
30
20
10
30
100
150
30
Offices
Cartography, designing, detailed
drafting
200
Accounting, auditing, tabulating,
book-keeping, business-machine
operation, reading poor
reproductions, rough layout
drafting
150
Regular office work, reading good
reproductions, reading or
transcribing handwriting in hard
pencil or on poor paper, active
filing, index references,
mail sorting
100
Reading or transcribing handwriting
in ink or medium pencil on
good-quality paper, intermittent
filing
70
Reading high-contrast or well-printed
material, tasks and areas not
involving critical or prolonged seeing
such as conferring, interviewing,
inactive files, and washrooms
30
Corridors, elevators, escalators,
stairways
20k
Packing and boxing (see Materials
handling)
Paint manufacturing
General
Comparing mix with standard
Paint shops
Dipping, simple spraying, firing
Rubbing, ordinary hand painting and
finishing art, stencil and special
spraying
Fine hand painting and finishing
Extra-fine hand painting and finishing
(automobile bodies, piano
cases, etc.)
30
200 j
50
50
100
300a
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.135
ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Paper-box manufacturing: general
manufacturing area
50
Paper manufacturing
Beaters, grinding, calendering
30
Finishing, cutting, trimming,
papermaking machines
50
Hand counting: wet end of paper
machine
70
Paper-machine reel, paper inspection,
laboratories
100
Rewinder
150
Plating
Polishing and burnishing
30
100
Power plants (see Central station)
Post offices
Lobby: on tables
Sorting, mailing, etc.
Printing industries
Type foundries
Matrix making, dressing type
Font assembly: sorting
Hand casting
Machine casting
Printing plants
Color inspection and appraisal
Machine composition
Composing room
Presses
Imposing stones
Proofreading
Electrotyping
Molding, routing, finishing,
leveling molds, trimming
Blocking, tinning
Electroplating, washing, backing
Photoengraving
Etching, staging
Blocking
Routing, finishing, proofing
Tint laying
Masking
Professional offices (see Hospitals)
30
100
100
50
50
50
200a
100
100
70
150
150
100
50
50
50
50
100
100
100
Area
Footcandles
on tasks*
Receiving and shipping (see Materials
handling)
Residences
Specific visual tasks l
Table games
30
Kitchen activities
Sink
70
Range and work surfaces
50
Laundry, trays, ironing board,
ironer
50
Reading and writing including
studying
Books, magazines, newspapers
30
Handwriting, reproduction and
poor copies
70
Desks, study
70
Reading music scores
Simple scores
30
Advanced scores
70
(When score is substandard size
and notations are printed on
the lines, 150 fc or more are
needed.)
Sewing
Dark fabrics (fine detail, low
contrast)
200
Prolonged periods (light to
medium fabrics)
100
Occasional periods (light fabrics) 50
Occasional periods (coarse thread,
large stitches, high-contrast
thread to fabric)
30
Shaving, makeup, grooming; on the
face at mirror locations
50
General lighting
Entrances, hallways, stairways, stair
landings
10m
Living room, dining room, bedroom,
family room, sunroom, library,
game or recreation room
10m
Kitchen, laundry, bathroom
30
Restaurants, lunchrooms, cafeterias
Dining areas
Cashier
Intimate type
Light environment
Subdued environment
50
10
3
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.136
DIVISION TEN
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
For cleaning
Leisure type
Light environment
Subdued environment
Quick-service type
Bright surroundingsn
Normal surroundingsn
Food displays: twice the general
levels but not under
Kitchen, commercial
Inspection, checking, pricing
Other areas
Rubber goods, mechanical
Stock preparation
Plasticating, milling, Banbury
Calendering
Fabric preparation: stock cutting and
hose looms
Extruded products
Molded products, curing
Inspection
20
30
15
100
50
50
70
30
30
50
50
50
50
200a
Rubber tire and tube manufacturing
Stock preparation
Plasticating, milling, Banbury
Calendering
Fabric preparation: stock cutting and
bead building
Tube and tread tubing machines
Tire building
Solid tires
Pneumatic tires
Curing department: tube, casing
Final inspection: tube, casing
Wrapping
30
50
70
200a
50
Sawmills: grading redwood lumber
300
Schools
Reading printed material
Reading pencil writing
Spirit-duplicated material
Good
Poor
Drafting, benchwork
Lip reading, chalkboards,
sewing
30
50
50
50
30
70
30
100
100a
150a
Area
Footcandles
on tasks*
Service space
Stairways
Elevators, freight and passenger
Corridors
Storage (see Storage rooms)
Toilets and washrooms
Service stations
Service bays
Salesroom
Shelving and displays
Rest rooms
Storage
Sheet-metal works
Miscellaneous machines, ordinary
benchwork
Presses, shears, stamps, spinning,
medium benchwork
Punches
Tinplate inspection, galvanized
Scribing
Shoe manufacturing. leather
Cutting, stitching
Cutting tables
Marking, buttonholing, skiving,
sorting, vamping. counting
Stitching: dark materials
Making and finishing: nailers, sole
layers welt beaters and scarfers,
trimmers, welters, lasters, edge
setters, sluggers, randers, wheelers,
treers, cleaning, spraying, buffing,
polishing, embossing
20
20
20
30
30
50
100
15
5
50
50
50
200 j
200 j
300a
300a
300a
200
Shoe manufacturing. rubber
Washing, coating, mill-run
compounding
30
Varnishing, vulcanizing, calendaring,
upper and sole cutting
50
Sole rolling, lining, making and
finishing processes
100
Show windowso
Daytime lighting
General
Feature
200
1000
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.137
ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Nighttime lighting
Main business districts (highly
competitive)
General
Feature
Secondary business districts or
small towns
General
Feature
Open-front stores (see Stores)
Soap manufacturing
Kettle houses. cutting, soap chips and
powder
Stamping, wrapping and packing,
filling, and packing soap powder
200
1000
100
500
30
50
Steel (see Iron and steel)
Storage-battery manufacturing: molding
of grids
Storage rooms or warehouses
Inactive
Active
Rough, bulky
Medium
Fine
Storeso
Circulation areas
Merchandising areas
Service
Self-service
Showcases and wall cases
Service
Self-service
Feature displays
Service
Self-service
Stockrooms
Footcandles
on tasks*
Structural-steel fabrication
Stairways (see Service space)
Stone crushing and screening
Bolt-conveyor tubes, main-line shafting
spaces, chute rooms. inside of bins
Primary breaker room, auxiliary
breakers under bins
Screens
Area
10
10
20
50
5
10
20
50
30
100
200
200
500
500
1000
30
50
Sugar refining
Grading
Color inspection
50
200
Testing
General
Extra-fine instruments, scales, etc.
50
200a
Textile mills: cotton
Opening, mixing, picking
Carding, drawing
Slubbing, roving, spinning,
spooling
Beaming and splashing on comb
Gray goods
Denims
Inspection:
Gray goods {hand turning)
Denims {rapidly moving)
Automatic tying-in
Weaving
Drawing-in by hand
Textile mills: silk and synthetics
Manufacturing: soaking, fugitive
tinting, conditioning or setting
of twist
Winding, twisting, rewinding and
coning, quilling, slashing
Light thread
Dark thread
Warping (silk or cotton system):
on creel, on running ends, on reel,
on beam, on warp at beaming
Drawing-in on heddles and reed
Weaving
Textile mills: woolen and worsted
Opening, blending, picking
Grading
Carding, combing, recombing,
gilling
Drawing
White
Colored
Spinning {frame)
White
Colored
30
50
50
50
150
100
500a
150a
100
200a
30
50
100
100
200a
100
30
100a
50
50
100
50
100
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.138
DIVISION TEN
220. Levels of illumination (Continued)
Area
Spinning (mule)
White
Colored
Twisting: white
Winding
White
Colored
Warping
White
White (at reed)
Colored
Colored (at reed)
Weaving
White
Colored
Gray-goods room
Burling
Sewing
Folding
Wet finishing
Fulling
Scouring
Crabbing
Drying
Dyeing
Dry finishing
Napping
Shearing
Conditioning
Pressing
Inspecting (perching)
Folding
Footcandles
on tasks*
50
100
50
30
50
50
100
100
300a
100
200
150a
300a
70
50
50
50
50
100a
70
100
70
70
2000a
70
Area
Theaters and motion-picture houses
Auditoriums
During intermission
During picture
Foyer
Lobby
Footcandles
on tasks*
5
0.1
5
20
Tobacco products
Drying, stripping, general
Grading, sorting
Toilets and washrooms
30
200a
30
Upholstering: automobile, coach,
furniture
100
Warehouses (see Storage rooms or
warehouses)
Welding
General illumination
Precision-manual arc welding
Woodworking
Rough sawing and bench work
Sizing, planing, rough sanding,
medium-quality machine work
and benchwork, gluing,
veneering, cooperage
Fine benchwork and machine
work, fine sanding and
finishing
50
1000a
30
50
100
Exterior lighting
Building
General construction
Excavation work
Building exteriors and monuments:
floodlighted
Bright surroundings
Light surfaces
Medium-light surfaces
Medium-dark surfaces
Dark surfaces
Dark surroundings
Light surfaces
Medium-light surfaces
10
2
15
20
30
50
5
10
Medium-dark surfaces
Dark surfaces
Bulletin and poster boards
Bright surroundings
Light surfaces
Dark surfaces
Dark surroundings
Light surfaces
Dark surfaces
Central station
Catwalks
Cinder dumps
Coal-storage area
15
20
50
100
20
50
2
0.1
0.1
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.139
ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Coal unloading
Dock (loading or unloading
zone)
Barge-storage area
Car dumper
Tipple
Conveyors
Entrances
Generating or service building
Main
Secondary
Gatehouse:
Pedestrian entrance
Conveyor entrance
Fence
Fuel-oil delivery headers
Oil-storage tanks
Open yard 0.2
Platforms: boiler, turbine deck
Roadway
Between or along buildings
Not bordered by buildings
Substation
General horizontal
Specific vertical (on disconnects)
Loading and unloading platforms
Freight-car interiors
5
0.5
0.5a
5
2
10
2
10
5
0.2
5
1
5
1
0.5
2
2
Coal yards (protective)
0.2
Dredging
2
Flags. floodlighted (see Bulletin and
poster boards)
Gardens
General lighting
Path, steps, away from house
Backgrounds: fences, walls, trees,
shrubbery
Flower beds, rock gardens
Trees, shrubbery, when
emphasized
Focal points, large
Focal points, small
0.5
1
2
5
5
10
20
Gasoline stations (see Service stations)
Highways
Footcandles
on tasks*
Area
q
20
10
Lumberyards
1
Parking lots
5
Piers
Freight
Passenger
20
20
Prison yards
5
Protective lighting
Boundaries
Glare-projection technique (isolated)
0.15
General-Iighting technique
(nonisolated)
0.20
Entrances
Active (pedestrian and/or conveyance) 5
Inactive (normally locked.
infrequently used)
1
Vital locations or structures
5
Building surrounds
1
Active shipping-area surrounds
5
Storage areas, active
20
Storage areas, inactive
1
Loading and unloading platforms
20
General inactive areas
0.20
Quarries
5
Railroad yards
Receiving
Classification
0.2
0.3
q
Roadways
Service stations (at grade)
Approach
Driveway
Pump-island area
Building faces (exclusive
of glass)
Service areas
Surroundings:
Dark
Light
1.5
3
1.5
5
20
30
10r
3
30r
7
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.140
DIVISION TEN
220. Levels of illumination (Continued)
Footcandles
on tasks*
Area
Shipyards
General
Ways
Fabrication areas
5
10
30
Footcandles
on tasks*
Area
Storage yards (active)
Streets
20
q
Water tanks with advertising messages
(see Bulletin and poster boards)
Smokestacks with advertising messages
(see Bulletin and poster boards)
Sports lighting
Archery
Shooting
Target
line
10r
10
5r
5
Tournament
Recreational
Badminton
Tournament
Club
Recreational
30
20
10
Infield Outfield
Baseball
Major league
AA and AAA leagues
A and B leagues
C and D leagues
Semiprofessional and
municipal leagues
Junior leagues (Class I
and Class II)
On seats during game
On seats before and after
game
150
75
50
30
100
50
30
20
20
15
40
30
2
5
Basketball
College and professional
College intramural and high
school with spectators
College intramural and high
school without spectators
Recreational (outdoor)
Lanes
50
30
10
Pins
20
10
50r
30r
Bowling
Tournament
Recreational
Bowling, lawn
Tournament
Recreational
10
5
Boxing or wrestling (ring)
Championship
Professional
Amateur
Seats during bout
Seats before and after bout
500
200
100
2
5
Pier or
dock
Casting
Bait
Dry-fly
Wet-fly
10
10
10
Target
5r
5r
5r
50
30
Croquet
Tournament
Recreational
20
10
45 m
(150 ft)
from
On land shore
Bathing beaches
Billiards (on table)
Tournament
Recreational
General area
1
3r
Curling: indoor
10
5
Tees
20
Rink
10
Football
(Index: Distance from nearest
sideline to the farthest row
of spectators.)
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.141
ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Class I: over 30 m (100 ft)
Class II: 15 to 30 m (50 to 100 ft)
Class III: 9 to 15 m (30 to 50 ft)
Class IV: under 9 m (30 ft)
Class V: no fixed seating facilities
100
50
30
20
10
It is generally conceded that the distance
between the spectators and the play
is the first consideration in determining
the class and lighting requirements.
However, the potential seating capacity
of the stands should also be considered,
and the following ratio is suggested:
Class I, for more than 30,000 spectators;
Class II, for 10,000 to 30,000;
Class III, for 5000 to 10,000; Class IV
for fewer than 5000 spectators
Golf driving
General on the tees
At 200 yd
Practice and putting green
10
5r
10
Gymnasiums (refer to individual sports
listed separately)
Exhibitions, matches
General exercising, recreation
Assemblies
Dances
Lockers, shower rooms
30
20
10
5
10
Handball
Tournament
Club
Recreational
30
20
10
Horseshoes
Tournament
Recreational
10
5
Ice hockey
College or professional
Amateur league
Recreational
50
20
10
Lacrosse
20
Quoits
Footcandles
on tasks*
Area
Racing
Bicycle
Motor (midget automobile or
motorcycle)
Horse
Dog
20
20
30
Rifle range
On target
Firing point
Range
50r
10
5
Roque
Tournament
Recreational
20
10
Shuffleboard
Tournament
Recreational
10
5
20
Skating
Roller rink
Ice rink (indoor or outdoor)
Lagoon, pond, or flooded area
5
5
1
Skeet shoot
Target: surface at 18 m (60 ft)
Firing point, general
30r
10
Ski-slope practice
0.5
Soccer
Professional and college
High school
Athletic field
30
20
10
Softball
5
Professional and
championship
Semiprofessional
Industrial league
Recreational
Squash
Tournament
Club
Recreational
Infield Outfield
50
30
30
20
10
20
15
7.5
30
20
10
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
10.142
DIVISION TEN
220. Levels of illumination (Continued)
Area
Swimming pools
General, overhead
Outdoors
Indoors
Tennis
Tournament
Club
Recreational
Footcandles
on tasks*
10
s
t
Lawn Table
30
50
20
30
10
20
Area
Footcandles
on tasks*
Trapshoot
Target [at 45 m (150 ft)]
Firing point, general
30r
10
Volleyball
Tournament
Recreational
20
10
Transportation lighting
Airplanes: passenger compartment
General
Reading at seat
Airports
Hangar apron
Terminal-building apron
Parking area
Loading area
Automobiles: license plates
Motor coaches
City driving
Country driving,
5
20
1
0.5
2
0.5
30
15
Railway passenger cars
Reading and writing
General
Detail
Washroom section
General
Mirror
Toilet section
Dining car
Taverns
Social areas
Steps and vestibules
15
30
5
15
10
20
10
Railway mail cars
Mailbag racks and letter cases
Mail storage
30
15
Rapid-transit cars
30
20
50
Ships
Living areas
Staterooms
Crew
Officers
Passengers
Berth, on reading plane
Mirrors, at face
Baths
Crew
Public
Officers
Passengers
Mirrors, at face
Passageways
Stair foyers: passengers
Stairs
Passengers
Crew
Entrance: passengers
Lounges: passengers and officers
Recreation rooms: crew
On tables
Dining room: passengers
Mess room: officers and crew
On tables
Libraries
For reading
Smoking rooms
Enclosed promenades: along inboard bulkhead for reading
Barbershop and beauty parlor
On subject
Cocktail lounges
5u
5u
5u
15
50
5
5
5
5
50
5
10
10
5
10v
10x
20
30
10w
10
15
10
30
5x
10
20
50
5w
*Minimum on the task at any time. For general notes see beginning of tabulation; for other notes see end of tabulation.
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ELECTRIC LIGHTING
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ELECTRIC LIGHTING
220. Levels of illumination (Continued)
Area
Footcandles
on tasks*
Bars
Ballrooms
Swimming pools, indoor beaches
Shopping areas
Theaters
During show
Intermission
Gymnasiums
Hospital
Operating room
Dental room
Dispensary
Wards
Doctor’s office
Waiting room
Radio room: passenger foyer
Passenger counter, purser’s office
Navigating areas
Wheelhouse (not used under way)
Chartroom
On chart table
Radar room
Gyro room
Radio room
Ship’s offices
On desks and worktables
For bookkeeping and auditing
Log room
On desk
Service areas
Galley
Laundry
Pantry
Sculleries
Food preparationu
5w
5w
10y
20u
0.1
5
20
50u
30u
30u
5u
20u
10x
10x
20
5
10
50
5
5
10u
20
50
50
10
50
20u
15u
15u
15u
20
Area
Footcandles
on tasks*
Food storage (nonrefrigeration)
Refrigerated spaces (ship’s stores)
Butcher shop
Print shop
Tailor shop
Post offices
Lockers
Telephone exchange
Storerooms
Operating areas
Engine rooms (working areas)
Boiler rooms (working areas)
Fan rooms
Motor-generator rooms
(cargo handling)
Generator and switchboard rooms
Windlass rooms
Switchboards: vertical illumination
At top 3
3 ft above deck
Steering-gear room
Pump room
Gage and control boards (vertical
illumination) on gages
Shaft alley
Dry-cargo holds (permanent fixture)
Refrigerated-cargo loading and
unloading
Workshops
On work
Cargo hatches
Over hatch area
Adjacent deck area
Trolley coaches and streetcars
5
5
15u
30u
50u
20u
3
10u
5
10u
10u
5
5
10
5
0
10
5
1
30
3
1u
3u
20
50
5
3
30
*Minimum on the task at any time. For general notes see beginning of tabulation.
a
Obtained with a combination of general lighting plus specialized supplementary lighting. Care should be taken to
keep within the recommended brightness ratios. These seeing tasks generally involve the discrimination of fine detail
for long periods of time and under conditions of poor contrast. To provide the required illumination, a combination of
the general lighting indicated and specialized supplementary lighting is necessary. The design and installation of the
combination system must provide not only a sufficient amount of light but also the proper direction of light, diffusion,
and eye protection. As far as possible it should eliminate direct and reflected glare as well as objectionable shadows.
b
Dark paintings with fine detail should have 2 to 3 times higher illumination.
c
In some cases, much more than 100 fc (108 dalx) is necessary to bring out the beauty of the statuary.
d
Reduced or dimmed during sermon, prelude, or meditation.
e
Two-thirds of this value if interior finishes are dark (less than 10 percent reflectance) to avoid high brightness
ratios, such as between hymn book pages and the surroundings. Careful brightness planning is essential for good
design.
f
Special lighting such that (1) the luminous area is large enough to cover the surface which is being inspected and
(2) the brightness is within the limits necessary to obtain comfortable contrast conditions. This involves the use of
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DIVISION TEN
sources of large area and relatively low brightness in which the source brightness is the principal factor rather than
the footcandles produced at a given point.
g
For close inspection, 50 fc (54 dalx).
h
Pencil handwriting and reading of reproductions and poor copies require 70 fc (75 dalx).
i
For close inspection, 50 fc (54 dalx). This maybe done in the bathroom. but if a dressing table is furnished, local
lighting should provide the level recommended.
j
The specular surface of the material may necessitate special consideration in selection and placement of lighting equipment or orientation of the work.
k
Or not less than one-fifth of the level in adjacent areas.
l
Brightness of visual task must be related to background brightness.
m
General lighting for these areas need not be uniform in character.
n
Including street and nearby establishments.
o
(1) Values are illumination on the merchandise on display or being appraised. The plane in which lighting is
important may vary from horizontal to vertical. (2) Specific appraisal areas involving difficult seeing maybe lighted
to substantially higher levels. (3) Color rendition of fluorescent lamps is important. Incandescent and fluorescent usually are combined for best appearance of merchandise. (4) Illumination may often be made nonuniform to fit merchandising layout.
p
Values based on a 25 percent reflectance, which is average for vegetation and typical outdoor surfaces. These
figures must be adjusted to specific reflectances of materials lighted for equivalent brightnesses. Levels give satisfactory brightness patterns when viewed from dimly lighted terraces or interiors. When viewed from dark areas, they
maybe reduced by at least one-half, or they may be doubled when a high key is desired.
q
See Sec. 232.
r
Vertical.
s
60 lamp lumens per square foot of surface.
t
100 lamp lumens per square foot of surface.
u
Supplementary lighting should be provided in this space to produce the higher levels of lighting required for
specific seeing tasks involved.
v
The installation should be such that the level of illumination can be increased to at least 40 fc (43 dalx) for daytime embarkation.
w
In public areas such as lounges, ballrooms, bars, smoking rooms, and dining rooms, the footcandle values may
vary widely, depending upon the atmosphere desired, the decorative scheme, and the use made of the room.
x
See footnotes u and w.
y
Also underwater lights and sunlamps.
INTERIOR-LIGHTING SUGGESTIONS
221. Residence lighting. In the lighting of the home, the decorative element should
predominate. The lighting must, however, comply with the general rules of lighting (Sec.
188) concerning color, shadows, glare, and illumination. A room in which yellow or red is
the predominant color gives a warm, cheerful impression, whereas a room furnished in blue
tends to produce the opposite sensation. Shade and softened shadows are preferable to
sharp shadows or to no shadows. It is especially important that any glare be minimized.
Luminous ceilings can be installed in such rooms as kitchens and bathrooms.
Detailed recommendations for residence lighting are given in a booklet prepared by the
Committee on Residence Lighting of the Illuminating Engineering Society and titled
Design Criteria for Lighting Interior Spaces.
Kitchen. The kitchen requires plenty of well-diffused light for timely preparation of
food without accidents. In most kitchens, general lighting from two 40-W fluorescent
lamps or two 150-W to four 100-W incandescent lamps will provide satisfactory general illumination. For very large kitchens, 80 to 120 W of fluorescent lighting or two
100-W incandescent lamps per 60 ft2 will be needed. Unless the room is very small with
light-colored walls and ceilings, the general illumination should be augmented by additional localized ceiling or bracket units. A single light in the center of the kitchen usually compels the cook to work entirely in his or her own shadow, whether at the range,
the sink, or the kitchen cabinet or table. A single fluorescent ceiling unit over the center
of the sink or a bracket at each side of the sink is nearly always necessary to eliminate
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.145
shadows and provide adequate illumination at the sink. Often it is advisable to locate
similar units at the range and counter work areas.
Bedroom. The illumination requirements of the bedroom are somewhat similar to those
of the kitchen. General illumination should be provided by means of a centrally located
ceiling unit of low brightness so that it will not be uncomfortable to the eyes of one lying
in bed. Additional illumination should be provided at the dresser or bureau by means of
either brackets or a portable lamp on each side of the mirror. A bracket or wall-mounted
fluorescent unit should be provided at the head of each bed unless localized table luminaires are used for providing illumination for reading at these locations. Better illumination for this purpose is generally obtained by a wall-mounted bracket or fluoresent units.
Living Room. Although ceiling fixtures have been eliminated in many living rooms, an
attractive, properly shielded fixture is a very effective method of obtaining the general
level of illumination needed for festive occasions. For a quiet evening at home a lower
level of general illumination can be obtained by means of the indirect type of floor and
table lamps. With their high efficiency and good color characteristics, compact fluorescent lamps with integral ballasts or ballast adapters should be considered for use in floor
and table lamps. The chief function of bracket lamps is ornamentation, and they should
not be relied upon to provide necessary light for useful purposes.
Dining Room. There are several satisfactory methods of illuminating the dining room,
the selection depending upon personal taste. General illumination may be provided by
means of a centrally located chandelier. It should be mounted 30 in (762 mm) above the
table in an 8-ft- (2.4-m-) ceiling room. In rooms with higher ceilings, the chandelier
should be raised 3 in (76 mm) for each foot. Recessed downlights can be used with
chandeliers for dramatic lighting of table settings. Cove lighting by means of fluorescent lamps concealed in a trough a few inches down from the ceiling may be used. Wall
brackets for decorative effects are also common.
Bathroom. In the bathroom illumination of the mirror requires the greatest consideration.
For the best illumination of the mirror three luminaires, one at each side of the mirror and
one mounted overhead, are needed. Fairly good results can be obtained with only two
units located one at each side of the mirror. If only one unit is used, it should be mounted
overhead and centered with respect to the mirror. For small bathrooms the mirror wall
brackets will supply sufficient general illumination for the rest of the room. In rooms of
any appreciable size a central enclosing unit should be used in addition to the bracket
lamps. A ceiling-mounted heat lamp will provide added comfort for the winter months.
222. Store lighting. The object of lighting in a store is twofold. Primarily, sufficient
illumination must be provided to enable articles for sale to be seen plainly, but of almost
equal importance is the advertising value. The lighting units should be so selected as to give
a pleasing and cheerful appearance to the store as a whole, without glare. Stores may be
divided into three classes: (1) the small store, in which efficiency is of first importance;
(2) the large store, such as a department store, in which efficiency is necessary on account of
the large areas to be lighted but in which it must be balanced by artistic appearance, the result
being a compromise between the two; and (3) shops, large or small, in which the articles for
sale are of a special type and the profits large enough so that even the most inefficient system can be afforded if it is sufficiently attractive to appeal to customers. The general requirements which must be satisfied are outlined separately in the following sections.
General Features of Store Lighting. General lighting best meets the requirements for
the lighting of stores. The lamps should be arranged symmetrically with respect to bays
or pillars. Direct glare must be very carefully avoided. The position of the counters need
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DIVISION TEN
not be considered in spacing the lamps. Local accurate-color–matching units are advisable at certain points in the store, such as counters for the sale of ribbon and dress goods.
The intensity of illumination must be varied with the articles which are to be sold.
Furniture requires well-diffused lighting of relatively low intensity. Colored dress
goods, men’s clothing, rugs and carpets, and so on, require a high intensity. In many
installations, side light is necessary and should be given special attention in selecting
types of units and reflectors. Crystal and jewelry should be so lighted as to sparkle and
glitter. Bare lamps and mirrored reflectors may be used in ornamental-type luminaires
for this purpose. In this case glare is to a certain extent unavoidable, but light units can
usually be so located as to be out of the range of vision of customers when they are
inspecting the wares on display.
Pictures require a high intensity, with the light units at such an angle that light will
not be reflected from the surface of the painting or from the glass directly into the
observer’s eyes. Individual units or mirrored-trough reflectors, with fluorescent or tubular tungsten lamps, are ordinarily used.
High-color-rendition fluorescent lamps should be used to illuminate all items in
which color is important, such as women’s dresses, coats, and furs, men’s suits and
coats, draperies and curtains, tapestries, and neckties. Concealed fluorescent units may
also be used in wall valances or coves for decorative effects.
Showcases. A showcase interior should have more illumination than the top of the case
but not more than about twice as much. If the illumination on top is in the 30- to 75-fc
(323- to 807-lx) range, T-6 or T-8 slimlines inside the case, operated at 200 mA, provide
sufficient light; for higher footcandles on the top, an operating current of 300 mA is sometimes recommended. Too great a differential between the illumination inside the case and
that on the top, where the merchandise is normally inspected more closely prior to purchase, is not advisable. Many products examined under an illumination level significantly
lower than that under which they were displayed lose some of their attraction. This is not
a consideration with feature displays, since they are seldom removed for inspection.
The plot in Fig. 10.109 indicates the approximate initial footcandles perpendicular to
the source at various angles for each 100 rated lamp lm/ft of case length. The figures above
the arcs represent footcandles obtained with a fluorescent lamp in a specular showcase
FIGURE 10.109 Initial footcandles for each 100 rated
lamp lm/ft of showcase length.
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ELECTRIC LIGHTING
reflector. The figures below the arcs represent footcandles obtained with standard filament
reflector showcase lamps and differ from the fluorescent values because of beam control.
Wall Cases. Wall cases generally should be illuminated to approximately the same level
as counter display areas. However, higher levels are desirable when the brightness of the
wall case and the adjoining sales space is to be used partly to pull traffic into the area. One
of the most important features of the lighting of wall cases for wearing apparel is that it
be designed to light the entire case from top to bottom rather than just the shoulders of the
garments. The illumination at the bottom should be at least one-tenth of that at the top.
The accompanying table lists the approximate illumination in footcandles produced
by fluorescent lamps on a vertical surface for each 100 rated lamp lm/ft of case length.
The specular symmetrical reflector was so adjusted that its maximum candlepower was
directed at a point 42 in (1067 mm) below the lamp. When no reflector was used, the
entire inner surface of the valance was painted white.
Horizontal distance–H, in
Vertical
distance–V, in
6
12
18
24
30
36
42
48
54
60
Values with
symmetrical reflector, fc
Values without
reflector, fc
6
12
18
24
6
12
18
24
21.4
12.0
7.4
4.4
2.6
2.0
1.4
0.8
0.8
0.6
15.7
12.8
9.6
6.9
4.8
3.8
2.8
1.9
1.6
1.2
12.1
12.1
10.0
8.8
6.9
5.2
4.1
2.8
2.4
1.9
9.8
10.2
9.1
7.7
6.8
6.1
5.0
4.1
3.4
2.6
30.6
11.3
5.2
2.6
1.4
1.0
0.6
0.4
0.4
0.3
22.8
14.7
8.8
5.0
3.3
2.2
1.4
1.0
0.8
0.8
16.5
13.6
10.2
6.6
4.4
3.2
2.2
1.6
1.4
1.0
13.5
12.2
9.6
7.2
5.2
4.1
3.0
2.2
1.6
1.4
223. Show-window lighting. Since the primary object of a show window is to
attract attention, it should be illuminated to a sufficient intensity so that it will stand out
from its surroundings. Several factors need to be considered in designing show-window
lighting systems such as type of merchandise, location of the store, time-of-day usage,
enclosed or open back design, and the size and shape of the show window. Great care
should be exercised in designing show-window lighting so that the lamps will be concealed
from view. The lighting equipment should be concealed either by recessing it in the ceiling
or by employing a valance between the reflector and the front glass of the window. A good
way to blind prospective customers so that they cannot see the goods on display in your
window is to put exposed lamps around the window borders, suspend them from chandeliers, or so install them in the top of the window that their eyes cannot escape them.
Shadows are necessary in window lighting to produce the desired effects, but they
should not be too sharply defined. The light should come from in front of the goods. If the
lamps are placed in the middle of the show-window ceiling, the front of the goods displayed
in the front of the window will be in darkness because of shadows they cast.
If the back of the display window is not boxed in or if the window back is of glass, a
valance or a curtain should be provided to screen the window lamps from the store and to
prevent back reflection to an observer on the sidewalk.
Customers’ attention should be attracted by illuminating selected articles with spotlights. If decorative effects are desired, colored spotlights may be used, and motor-operated
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DIVISION TEN
dimmers can add motion and dramatic effects. Fluorescent units bring out the beauty of floral displays and emit very little heat. Daylight lamps bring out the beauty of polished aluminum and chromium-plated articles.
224. Show-window lighting equipment. Incandescent lamps are extensively
used in show-window applications owing to the wide variety of wattages, sizes, reflectorized types, and colored lamps. Lighting units with special reflectors for show-window
lighting are available in many shapes to meet the varied requirements of different types and
sizes of windows. Reflectorized (reflector and projector) lamps are widely used owing to
the built-in light control within the lamp. Low-voltage PAR and MR-16 reflector lamps
provide excellent beam control for lighting special areas of a show window to a higher
intensity. Colored reflector and PAR lamps or the use of colored gelatin screen or glass
roundels can provide desired effects with color. No general rules for shadows and color of
light to be used can be given. An infinite number of effects can be obtained. By experiment,
the display manager should determine the best effect for each display to be lighted.
225. School and office lighting. As school and office work is usually performed
during daylight hours, any artificial illumination is usually in conjunction with available
daylight. Since practically all the work done in an office or school is on plane surfaces such
as papers and books, shadows not only are unnecessary but are objectionable. Also, since
the persons must use artificial illumination for long periods of time, the glare should be
minimal. These requirements render indirect and semi-indirect units especially suitable for
office and school illumination. The units should, as a general rule, be more closely spaced
than for other classes of service. This spacing will produce a more gradual shading of any
shadows and will also afford a greater flexibility in desk and partition arrangement. The
extensive use of video-display units in offices and classrooms has established the need to
design lighting systems to avoid reflected brightness in VDU screens.
226. Lighting Codes and Legislation. Codes and regulations relating to lighting
generally fall within two categories: energy saving codes and safety and construction
codes. Energy saving codes are concerned with methods to conserve energy through the
efficient use of electric lighting. The codes establish maximum limits for power density
values (watts per square foot) for lighting used in various applications. In addition there
may also be codes which set minimum efficiency standards for lighting equipment.
The safety and construction codes involve the safety and construction requirements which
must be complied with in the construction, installation, and maintenance of lighting systems.
Contractors involved with lighting should be familiar with the codes and regulations
which are applicable in the geographic areas of their work.
HEAT WITH LIGHT FOR BUILDING SPACES
227. Luminaires for environmental control. Not too many years ago architects
designed buildings primarily as space enclosures. The end use for which the space enclosures
were intended usually dictated the type and design of the buildings and the division and arrangement of the space. Comfort conditioning of the space for people normally consisted of a heating
system for use in cold weather and a ventilating or air-conditioning system for warm weather.
Progress in building design and construction and in technological developments in
space conditioning has changed the architects’ objective in the design of buildings. Present
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10.149
emphasis is not only on space enclosure tailored to the needs of occupants but also on environment and environmental control of lighting, heating, cooling, acoustics, space flexibility,
and appearance (pleasing colors, etc.).
Visual and thermal conditions have become two of the most important considerations
in planned interior environment. Visual comfort is controlled primarily by quality and
quantity of illumination. And adequate illumination of proper quality for high visual performance and high visual comfort increases electric-energy loads, which also means higher
heat gain. Thus, lighting systems that provide adequate quality illumination may have a
considerable effect on thermal conditions within buildings. Thermal comfort is controlled
through a proper balance in temperature, relative humidity, and air motion. Accordingly,
light- and heat-producing characteristics of the lighting system have become dominant
factors in the thermal equation.
This expanded use of lighting heat heralds a new era in environmental design. It provides the opportunity to supply all or a substantial part of a building’s heating requirements
from lighting systems with accompanying benefits, and control of lighting heat is necessary for the most effective utilization of this energy.
228. Integrated lighting-heating-cooling systems. There has been a growing
coordinated activity between electrical and mechanical engineers since 1958, when the
Illuminating Engineering Society adopted new and higher recommended levels of illumination for most seeing tasks. This activity has resulted in many new techniques for handling
lighting heat loads, which are based on the integration and correlation of lighting, heating,
and cooling systems. Although many approaches to this problem are possible, the basic one
is to divert all possible lighting heat gain from the occupied spaces in buildings to keep the
capacity of the cooling system as low as possible. Another objective is to recapture some
or all of this lighting heat gain to keep the capacity of the heating system as low as possible. This heat may be removed from interior areas of the building which need cooling, for
example, and redirected to perimeter areas which need heating at the same time.
229. Air-handling troffers. In the typical integrated system, heat from the lighting
system is removed by passing return air from the air-conditioned space through vents integral with the luminaires over the warm surfaces of lamps, ballasts, and luminaires, into the
plenum or return air duct, and back through the return side of the air-conditioning system.
After tempering, the supply air is redistributed, entering the conditioned spaces through a
different set of vents, which are also integral with the luminaires. Luminaires designed for
this purpose are called air-handling troffers. There is also available an air-water luminaire,
in which circulating water through the luminaire removes the lighting heat.
By combining lighting, heating, and cooling services in a single outlet element (the
luminaire), the conflict for space both above and on the ceiling is reduced. This integration
forces coordinated design and produces as its visual result an architecturally clean, uncluttered
ceiling.
Many lighting manufacturers now have available air-handling troffers in a range of sizes
and for a variety of air-handling requirements: (1) static (non-air-handling), (2) air supply,
(3) air return, and (4) a combination of air supply and air return. These luminaires may be
integrated with either cooling systems or heating systems, or both. Installation methods
conform generally to those for standard fluorescent troffers.
Also available are several complete ceiling systems combining both air-supply and
air-return provisions, some of which use conventional fluorescent luminaires and some of
which incorporate special air-handling luminaires that are an integral part of the ceiling
system. Typical examples are shown in Figs. 10.110, 10.111, and 10.112. The air-handling
troffer in Fig. 10.110 supplies cool air to the occupied space below the ceiling and returns
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DIVISION TEN
FIGURE 10.110 Air-handling troffer. [Day-Brite Lighting Division, Emerson Electric Co., Electrical
Construction and Maintenance]
FIGURE 10.111 Unified ceiling system. [Day-Brite Lighting Division, Emerson Electric Co.]
FIGURE 10.112 Recessed incandescent downlights integrated with heating and cooling systems.
warm air from the occupied space through the
troffer to the open plenum above. Heat from
lamps and ballasts is also removed. Warm
plenum air may be discarded or mixed with
fresh air and recirculated for heating specific
occupied spaces.
The unified ceiling system in Fig. 10.111
provides complete environmental control
through a modular-size integrated package.
Each module combines lighting, heating,
cooling, sound control, partition tracks for
flexibility, shielding of the lighted portion of
a luminaire in the line of vision, and good
appearance.
The recessed incandescent downlight
(Fig. 10.112) is integrated with heating and
cooling systems to the extent that lighting
heat may be exhausted to the plenum space
and discharged as waste or reused.
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ELECTRIC LIGHTING
10.151
STREET LIGHTING
230. General requirements for street lighting. Good roadway lighting, often
termed traffic safety lighting, not only promotes safer conditions for drivers but provides
greater safety for pedestrians as well. It enhances the community value of a street by its
attractive appearance, which is usually reflected in higher property values. Well-lighted
streets also act as a deterrent to criminal activity.
To achieve truly effective street lighting it is essential that the installation be well
planned. Planned street lighting should follow the American Standard Practice for
Roadway Lighting of the Illuminating Engineering Society and will involve the following
considerations:
1.
2.
3.
4.
Traffic classification of the street.
Determination of the proper lighting intensity for the street classification.
Selection of luminaires according to the light distribution needed for the street.
Determination of the mounting height of the luminaire above the road surface and the
proper linear spacing between luminaries.
Each step follows the preceding one in logical order, and the following information will
assist in the planning of an installation. Manufacturers of roadway lighting equipment have
computerized programs to assist in detailed planning of an installation.
231. Roadway classification. A traffic classification relating to use should be made
of all streets so that the lighting-system design will be in keeping with the particular needs
of each street or highway. It is also recommended that roadways be classified by the area
of location to establish the volume of pedestrian traffic to be considered. Typical roadway
and area classifications are defined here (General Electric Co.).
Roadway Class
1. Freeway. A divided major roadway with full control of access and with no crossings
at grade. This definition applies to toll as well as to nontoll roads.
2. Expressway. A divided major roadway for through traffic with partial control of
access and generally with interchanges at major crossroads. Expressways for
noncommercial traffic within parks and parklike areas are generally known as
parkways.
3. Major roadways. The part of the roadway system that serves as the principal network
for through-traffic flow. The routes connect areas of principal traffic generation and
important rural highways entering the city.
4. Collector roadways. The distributor and collector roadways serving traffic between
major and local roadways. These are roadways used mainly for traffic movements
within residential, commercial, and industrial areas.
5. Local roadways. Roadways used primarily for direct access to residential, commercial, industrial, or other abutting property. They do not include roadways carrying
through traffic. Long local roadways will generally be divided into short sections by
collector roadway systems.
Area Class
1. Commercial. That portion of a municipality in a business development where ordinarily there are large numbers of pedestrians and heavy demand for parking space
during periods of peak traffic or sustained high pedestrian volume and continuously
heavy demand for off-street parking during business hours. This definition applies
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DIVISION TEN
to densely developed business areas outside, as well as those that are within, the central part of a municipality.
2. Intermediate. That portion of a municipality which is outside a downtown area but
generally within the zone of influence of a business or industrial development, characterized often by moderately heavy nighttime pedestrian traffic and somewhat
lower parking turnover than is found in a commercial area. This definition includes
densely developed apartment areas, hospitals, public libraries, and neighborhood
recreational centers.
3. Residential. A residential development, or a mixture of residential and commercial
establishments, characterized by few pedestrians and lower parking demand or
turnover at night. This definition includes areas with single-family homes, townhouses, and/or small apartments. Regional parks, cemeteries, and vacant lands are
also included.
232. Lighting intensity. The recommended illumination level is dependent both on
the area and on the roadway classification. Recommended minimum average maintained
levels and recommended average-to-minimum uniformity ratios for several classifications
are shown in the following table.
ANSI-IES Recommendations
Roadway classification
Minimum average
maintained footcandles
Uniformity, average
footcandles/minimum footcandles
Residential areas
Local
Collector
Major
0.4
0.6
1.0
6:1
3:1
3:1
Intermediate areas
Local
Collector
Major
0.6
0.9
1.4
3:1
3:1
3:1
Commercial areas
Collector
Major
1.2
2.0
3:1
3:1
233. Selection of luminaire. Luminaires should be selected according to their pattern of light distribution so as to conform not only to the light intensity required but to the
physical characteristics of the street to be lighted. Typical lateral candlepower distribution
curves for several types of luminaires are shown. Lateral beam width is measured to half
maximum candlepower.
Type I Luminaire. Type I is a two-way lateral distribution having a preferred lateral
width of 15 on each side of the reference line (total, 30), with an acceptable range of
from 10 to less than 20. It projects two beams in opposite directions along the roadway
parallel to the curbline. The candlepower distribution is similar on both sides of the
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10.153
vertical plane of maximum candlepower. Luminaires with this type of distribution are
generally applicable to locations near the center of a roadway where the mounting
height is approximately equal to the roadway width.
Four-Way Type I Luminaire. Four-way Type I is a distribution having four principal
concentrations at lateral angles of approximately 90 to one another, each with a width
of from 20 to less than 40 as in Type I. This distribution is generally applicable to
luminaires located over or near the center of a right-angle intersection.
Type II Luminaire. Type II distributions have a preferred lateral width of 25 with an
acceptable range of from 20 to less than 30. This distribution is generally applicable
to luminaires located at or near the side of relatively narrow roadways when the width
of the roadway does not exceed 1.6 times the mounting height.
Four-Way Type II Luminaire. Four-way Type II distributions have four principal light
concentrations, each with a width of from 20 to less than 30 as in Type II. This distribution is generally applicable to luminaire locations near one corner of a right-angle
intersection.
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DIVISION TEN
Type III Luminaire. Type III distributions have a preferred lateral width of 40 with an
acceptable range of from 30 to less than 50. This type of distribution is intended for
luminaires mounted at or near the side of medium-width roadways when the width of
the roadway does not exceed 2.7 times the mounting height.
Type IV Luminaire. Type IV distributions have a preferred lateral width of 60 with an
acceptable width of 50 or more. This type of distribution is intended for side-of-road
mounting and is generally used on wide roadways (width up to 3.7 times the mounting
height).
Type V Luminaire. Type V distribution is essentially circular, with equal candlepower at all lateral angles. This type of distribution is intended for luminaire mounting at or near the center of a roadway, in the center islands of parkways, and at
intersections.
234. Mounting height and spacing of luminaires. Two considerations are of
paramount importance in determining optimum mounting height: the desirability of minimizing direct glare from the luminaire and the need for a reasonably uniform distribution
of illumination on the street surface. The higher the luminaire is mounted, the farther it is
above the normal line of vision and the less glare it creates. However, the attainment of uniform illumination requires a certain relationship between mounting height, luminaire spacing, and the vertical angle of maximum candlepower for the specific luminaire (usually
between 70 and 80).
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10.155
For a given luminaire the ratio of pole spacing to mounting height should be low enough
so that the light at the angle of maximum vertical candlepower will strike the street at least
halfway to the adjacent pole. To provide greater uniformity on busy streets the spacing is
often reduced by as much as 50 percent, which provides a 100 percent overlap of vertical
beams.
The mounting heights recommended by the Illuminating Engineering Society’s
Roadway Lighting Committee take into account both the objective of minimum glare and
that of maximum uniformity. Greater mounting heights may often be preferable, but
heights less than those recommended should be avoided.
FLOODLIGHTING
235. Modern floodlighting meets many utilitarian requirements as well as many
applications concerned with decoration, aesthetics, or advertising values. Protecting property after nightfall, completing a construction job within the time allotted, illuminating a
dangerous traffic intersection, and prolonging the hours of play in recreational areas are
only a few of the almost infinite applications of utilitarian floodlighting.
As an advertising medium that compels attention without detracting from the beauty or
dignity of a building, floodlighting offers its best proof by the many excellent examples to
be found in almost every city. The natural beauty of churches, civic buildings, monuments,
and gardens is often enhanced by skillfully applied floodlighting.
236. Floodlighting design. The type of area to be lighted, the possible location of
equipment, and the variation in surrounding conditions impose problems in design which
tend to make floodlighting-design standardization difficult. Manufacturers of floodlighting
equipment can be consulted for detailed design information. There are, however, certain
basic rules which may be followed in installation design.
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DIVISION TEN
237. Step 1: Determine the level of illumination. In Table 220 are listed the illumination levels for many floodlighting applications. These levels are designated as footcandles in service, and allowance must be made for reasonable depreciation in the original
design.
In lighting buildings, monuments, etc., the reflection factor of the object and the brightness of the surroundings must be considered to determine the amount of light necessary
(Table 238).
238. Recommended Illumination Levels for Floodlighting
(IES Lighting Handbook)
Surround
Bright
Surface material
Light marble, white or cream terracotta, white plaster
Concrete, tinted stucco, light gray and buff
limestone, buff face brick
Medium gray limestone, common tan brick, sandstone
Common red brick, brownstone, stained wood
shingles, dark gray brick
Reflectance, %
Dark
Recommended level, fc
70–85
45–70
15
20
5
10
20–45
10–20a
30
50
15
20
a
Buildings or areas of materials having a reflectance of less than 20% usually cannot be floodlighted economically unless they carry a large amount of high-reflectance trim.
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239. Recommendations for Sports Lighting
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DIVISION TEN
240. Step 2: Determine the type and location of floodlights. Floodlighting
equipment may be of either the general-purpose or the heavy-duty class. The generalpurpose floodlight is one in which the inner surface of the housing serves as the reflecting
surface. The heavy-duty floodlight is more rugged, since its aluminum or glass reflector is
protected by a metal housing.
The finish of the reflector has an important influence on the beam spread. Most enclosed
units are available with either a narrow-beam (specular-finish) or a wide-beam (diffusefinish) reflector. Essentially all floodlighting equipment is enclosed today for improved
maintenance.
241. Data on Typical Floodlight Equipment
Description
Group A
Heavy-duty or
general-purpose
Group B
Heavy-duty
high-wattage HID
Group C
Heavy-duty
low-wattage HID
Group D
Heavy-duty
tungsten-halogen
Advantages
Lamp types
Beam-spread
NEMA typea
Good light control for
distance
Weathertight
Useful in a variety of
applications, mostly
sports lighting
1000- to 1500-W
metal halide
400- to 1000-W
high pressure sodium
1–5
Good light control
Weathertight
Easily serviced
High fixture efficiency
250-, 400-, and
1000-W metal halide
62
65
66
67
Good light control
Weathertight
Easily serviced
High fixture efficiency
Use at lower mounting or
where lower lighting
levels are satisfactory
175-W metal halide
35- through 250-W
high-pressure sodium
66
76
77
Good light control
Weathertight
Easily serviced
Low cost
300-, 500-, 1000-W,
and 1500-W, tungsten
halogen
64
65
250-, 400-, and 1000-W
high-pressure sodium
a
Asymmetrical beam spreads have a horizontal and a vertical designation. The horizontal is stated first; i.e., a
6 2 beam spread is a NEMA Type 6 in the horizontal dimension and a NEMA Type 2 in the vertical dimension.
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ELECTRIC LIGHTING
242. To simplify the specification of equipment the National Electrical
Manufacturers Association has introduced a series of type numbers specifying beam spread
and group letters specifying floodlight construction. To meet NEMA standards a floodlight
must conform to certain construction requirements as well as have a certain minimum efficiency for a given beam spread.
Although the choice of beam spread for a particular application depends upon individual circumstances, the following general principles apply;
1. The greater the distance from the floodlight to the area to be lighted, the narrower the
beam spread desired.
2. Since by definition the candlepower at the edge of a floodlight beam is 10 percent of the
candlepower near the center of the beam, the illumination level at the edge of the beam
is one-tenth or less of that at the center. To obtain reasonable uniformity of illumination
the beams of individual floodlights must overlap each other as well as the edge of the
surface to be lighted.
3. The percentage of beam lumens falling outside the area to be lighted is usually lower
with narrow-beam units than with wide-beam units. Thus narrow-beam floodlights are
preferable when they will provide the necessary degree of uniformity of illumination
and the proper footcandle level.
Outdoor Floodlighting Designations
Beam spread,
NEMA type
10–18
18–29
29–46
46–70
70–100
100–130
130 and up
1
2
3
4
5
6
7
243. Typical Floodlighting Applications
Application
Location of equipment
Class of equipment
At edge of area and mounted as high as
possible.
Spacing not to exceed
4 times mounting height.
General-purpose enclosed
or heavy-duty
Type 4, 5, or 6
Immediately inside and below concealing
parapet—maximum distance from face
of building to be lighted.
Heavy-duty or generalpurpose
Type 3, 4, or 5
In banks at suitable location. One bank
normally should cover an area whose
height and length are not greater than
the distance from the units to the face
of the building.
Heavy-duty or general
purpose
Type 1, 2, 3, or 4
At edge of area where they will not hinder
traffic. Minimum mounting height 20 ft.
Heavy-duty
Type 5 or 6
On ground 5 to 25 ft from vertical
surface, concealed by hedge, low
structure, or natural elevation.
Heavy-duty or general
purpose
Type 3, 4, 5, or 6
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DIVISION TEN
The location of floodlighting equipment is usually dictated by the type of application
and the physical surroundings. If the area is large, individual towers or poles spaced at regular intervals may be required to light it evenly; smaller areas may require only one tower
with all equipment concentrated on it, or adjacent buildings may be utilized as floodlight
locations. The accompanying chart will aid in the selection of the right equipment and its
proper location for a number of typical floodlighting applications.
In planning any floodlighting system it is important that the light be properly controlled.
Strong light directed parallel to a highway or a railroad track can be a dangerous source of
glare to oncoming traffic, and light thrown indiscriminately on adjacent property may be a
serious nuisance.
244. Step 3: Determine the coefficient of beam utilization. To determine the
number of floodlights that will be required to produce a specified level of illumination in a
given situation, it is necessary to know the number of lumens in the beam of the floodlights
and the percentage of the beam lumens striking the area to be lighted. The beam lumens can
be obtained from the manufacturer’s catalog. The ratio of the lumens striking the floodlighted surface to the beam lumens is called the coefficient of beam utilization. (CBU). If
an area is uniformly lighted, the average CBU of the floodlights in the installation is always
less than 1.0.
The coefficient of beam utilization for any individual floodlight will depend on its location, the point at which it is aimed, and the distribution of light within its beam. In general,
it may be said that the average CBU of all the floodlights in an installation should fall
within the range of 0.60 to 0.90. Utilization of less than 60 percent of the beam lumens is a
definite indication that a more economical lighting plan should be possible by using different locations or narrower-beam floodlights. On the other hand, if the CBU is over 0.90,
the beam spread selected probably is too narrow and the resultant illumination will be
spotty. Accurate determination of the CBU is possible only after the aiming points have
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ELECTRIC LIGHTING
been selected. However, an estimated CBU can be determined by experience or by making
calculations for several potential among aiming points and using the average figure thus
obtained.
To make such calculations the floodlighted area is superimposed on the photometric
grid and the ratio of the lumens inside this area to the total beam lumens is determined.
All horizontal lines on a building (or straight lines on a ground area which are parallel
to a line perpendicular to the beam axis) appear as straight horizontal lines on the grid
if the floodlight is so aimed that its beam axis is perpendicular to a horizontal line on the
face of the building. All vertical lines except the one through the beam axis appear
slightly curved.
245. Step 4: Estimate the maintenance factor. Lighting efficiency is seriously
impaired by blackened lamps and by dirt on the reflecting and transmitting surfaces of the
equipment. To compensate for the gradual depreciation of illumination on the floodlighted
area, a maintenance factor must be applied in the calculations to make allowance for the
following:
1. Loss of light output due to dirt on the lamp, reflector, and cover glass.
2. Loss in light output of the lamp with life. Because some of the light must pass through
the bulb more than once before finally leaving the floodlight, bulb blackening also lowers
floodlight efficiency, the reduction in beam lumens being about double the reduction in
bare-lamp output.
A maintenance factor of 0.75 has been widely used for floodlights.
However, if the atmosphere is not clean, if the floodlights are cleaned infrequently, or
if lamps are replaced only on burnout, a realistic appraisal of in-service conditions will
require the use of considerably lower maintenance factors. Differences in lumen maintenance among lamp types and sizes should also be considered. With incandescent lamps the
higher the wattage for a given bulb size or the smaller the bulb for a given wattage, the
denser the bulb blackening and the greater the depreciation in light output.
Approximate Average Lamp Lumens throughout Life
Lamp type
Standard incandescent
Tungsten-halogen incandescent
Mercury
Metal halide
High-pressure sodium
% of Initial lumens
83
98
60
80
90
With narrow-beam floodlights, dirt on the reflector and cover glass tends to widen the
beam spread, reducing the maximum candlepower more than the total light output. Thus
for a small lighted area utilizing only the central part of a beam (e.g., a 4-ft, or 1.2-m)
archery target at 100 yd, or 91.4 m), a smaller percentage of the beam lumens will strike
the target after the floodlight has become dirty. Therefore the depreciation in footcandle
intensity will be greater than the depreciation in total light output, and it will be necessary
to consider this in selecting a maintenance factor.
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DIVISION TEN
246. Step 5: Determine the number of floodlights required.
Number of floodlights area footcandles
beam lumens CBU MF
(18)
where area is the surface area to be lighted in square feet and footcandles are as selected
from Table 238. For beam lumens, refer to the manufacturer’s catalog for the equipment
under consideration. If the lamps are to be burned at other than rated voltage, the beam
lumens, and hence the number of floodlights required, is altered. The increase in lumen output for 5 and 10 percent overvoltage operation is indicated in Sec. 249. For the CBU (coefficient of beam utilization), refer to step 3; and for the MF (maintenance factor), to step 4.
247. Step 6: Check for coverage and uniformity. After a tentative layout has
been made (steps 1 to 5), uniformity can be checked by calculating the intensity of illuminatin at a few points on the floodlighted surface. This may be done by the point-by-point
method described in Sec. 204, using either a candlepower-distribution curve or an isocandle diagram. If uniformity is found to be unsatisfactory, a larger number of units may have
to be used.
248. Application notes
Type of Light Source. Most floodlighting installations today utilize high-intensity–
discharge lamps owing to their higher efficacy and long lamp life. Where incandescent
lamps are used, they are generally the tungsten-halogen types.
Buildings and Monuments. The floodlighting of a building or a monument is primarily a problem in aesthetics, and each installation must be studied individually. Under
some circumstances, particularly with small utilitarian buildings or larger buildings
which lack special architectural features, uniform illumination is desirable. To create an
appearance of uniform brightness over the entire facade of a building, it is usually necessary to increase the actual brightness appreciably toward the top. Higher brightness at
the top of a building also increases its apparent height.
With buildings of classical design or special architectural character uniform illumination often defeats the purpose of the lighting, which should aim to preserve and
emphasize the architectural form. Buildings are designed primarily for daytime appearance, when the light comes from above. This effect is almost impossible to duplicate
with floodlights, which must be mounted in nearby locations and usually at a height no
greater than the elevation of the building. However, it is often possible to achieve a
result that is interesting and pleasing, although quite different from the daytime appearance. Shadows are essential to relief, and contrasts in brightness levels or sometimes in
color can be used advantageously to bring out important details and to suppress others.
Sculpture or architectural details require particularly careful treatment to avoid flatness
or grotesque shadows that may entirely distort the appearance as it has been conceived
by the artist or architect.
Excavation and Construction. Approximately one 1500-W tungsten-halogen, one
400-W metal halide or HPS, or two 250-W metal halide or HPS units will be required
for each 5000 ft2 (465 m2) of excavation area or for each 1000 to 2000 ft2 (93 to 186 m2)
of construction area. It is usually most satisfactory to mount floodlights in groups of two
or more on wood poles or towers 40 to 70 ft (12.2 to 21.3 m) above ground. A minimum
of two poles should be used, with enough poles on larger jobs to provide coverage at
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10.163
any working point from two or three floodlight banks. Fixed-pole spacing may be from
11/2 to 3 times mounting height and as much as 5 times mounting height on large projects. Occasionally it is practical to provide one or two portable poles mounted on
timber-sled bases. If a mechanical shovel or crane is used, it is advisable to mount an
automatic leveling floodlight on the boom.
Directional Application Such as Railway Yards and Freight Terminals. There are
two general types of railway-yard lighting, the unidirectional system and the parallel
opposing system. The first is applicable only to tracks on which the traffic is all in one
direction, the light being directed with the traffic flow. Glare is entirely eliminated, but
seeing is entirely by direct light without the advantages of silhouette effect. The parallel oppositing system is used when the traffic flows in both directions. Here seeing is
accomplished by direct light from the tower behind the observer and by the silhouette
of cars and glint from the rails produced by light from the tower ahead of the observer.
Tower locations are determined by track layouts and operating methods, but in general spacings should not exceed 1000 to 2000 ft (305 to 610 m) for the parallel opposing system or 800 to 1000 ft (245 to 305 m) for the unidirectional system. The first tower
in the classification yard should be near the ladder tracks but on the approach side of the
hump, so that spill light or a separate floodlight, if necessary, illuminates the hump area.
Narrow yards can be lighted by single towers located in the center. Wide yards should
have pairs of towers opposite each other, each about one-fourth of the yard width from
the edge. Except for spacings well below the values noted above, 90 ft (36 m) should be
considered a minimum mounting height.
The lighting of outdoor freight terminals without covered platforms is similar to that
of railroad yards except that the intensities must be much higher. Poles must be placed
at the ends of the platforms to prevent interference with vehicular traffic and in line with
the platforms to avoid shadows thrown by cars standing on the tracks. Mounting heights
of from 60 to 80 ft (18 to 24 m), depending on the average length of throw, are required.
Heavy-duty floodlights are recommended for all railroad service.
Color. Color is provided in floodlight installations usually by colored cover glass,
which is generally available for enclosed floodlights to replace regular lenses. When
smaller amounts of colored light are needed, colored R or PAR incandescent lamps may
be used. Any color of filter absorbs a large amount of light, and this loss must be considered in designing the installation. The following approximate transmission values are
found in typical commercial color filters: amber, 40 to 60 percent; red, 10 to 20 percent;
green, 5 to 20 percent; and blue, 3 to 10 percent. Although less colored light than white
light is usually required for equal advertising or decorative effectiveness, it is desirable
to determine by experiment the exact amount of colored light necessary for any particular application.
The color of light from high-intensity–discharge light sources is particularly desirable in specific decorative floodlighting applications. Metal halide and phosphor-coated
mercury lamps are used where a cooler color of light is preferred, while high-pressure
sodium lamps are applied in installations better suited to a warmer tone. Clear mercury
lamps are very effective in floodlighting trees and landscaping owing to the greenishblue character of the light from these lamps.
249. Sports Lighting. The level of illumination required depends upon several factors, among which are the speed of the game, the skill of the players, and the number of
spectators and their distance from the field of play. If television coverage is involved, this
also affects the lighting level. Economic considerations also are important. High intensities
of illumination are desirable in almost all sports, but since lower levels are acceptable, a
variety of layouts are suggested.
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DIVISION TEN
HID lighting systems with metal halide and high-pressure sodium lamps are extensively
used in sports lighting owing to their high efficacy and longer lamp life. The warm-up and
restrike characteristics of these light sources should be recognized in designing the lighting
system. A standby incandescent system may be desired in spectator areas.
Incandescent lighting systems are still used in sports-lighting applications owing to the
lower system cost when the annual hours of usage are limited. In sports installations in
which the lighting is operated during fewer than about 500 h per year, it may be economical to use short-life incandescent lamps or to burn standard lamps at higher than rated voltages. This reduces the power cost and the required number of floodlights. For fewer than
200 h per season, general-service incandescent lamps at 10 percent overvoltage are generally used. If the system is used between 200 and 500 h per year, operation of general-service
lamps at 5 percent overvoltage is preferable. The following table shows the effect of overvoltage operation on the life, wattage, and light output of 1000- and 1500-W incandescent
lamps.
Approximate Performance of 1000- and 1500-W Incandescent Lamps
Voltage
Rated
5% over rated
10% over rated
Light, %
Watts, %
Lamp life, %
100
117
135
100
108
116
100
50
30
The layouts that follow are guidelines to obtain the recommended levels of illumination
if high-quality floodlights are mounted and operated as indicated. Some latitude in beamspread requirements is acceptable when several floodlights are mounted on a single pole,
provided the resulting average beam spread is approximately the same as that specified.
NOTE For current recommended practice on sports lighting, consult Illuminating
Engineering Society, IES Sports Lighting, RP-6.
250. Archery
The floodlight provides visibility of the arrow throughout flight.
Floodlights
Lamps
Mounting height
Poles
Per target
One Type 2, Group A
One Type 6 5, Group B
For enclosed floodlight
Distance up to 30 yd: 175-W metal halide
30 to 50 yd: 250-W metal halide
50 to 100 yd: 400-W metal halide
Enclosed floodlight 15 ft above ground
Flood on same pole 12 ft above ground
One per target
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ELECTRIC LIGHTING
251. Badminton
Indoor courts may be lighted with industrial diffusing units along the sidelines.
Floodlights
Class
Type
Group
No. per
pole
Total no.
Lamp watts
Total load,
kW
Recreational
65
D
2
4
500
2
Lamps
Mounting height
Poles
500-W tungsten-halogen
20 to 25 ft above court
Two per court
252. Baseball
Floodlights
Poles
Class
Type
Group
A’s
B’s
C’s
Total
no.
Major league
AAA and AA
A and B
C and D
Semipro and municipal
2
2, 3
2, 3
3, 5
5
A
A
A
A
A
…a
12
10
6
4
…a
24
16
8
6
…a
18
8
6
4
…a
144
84
52
36
aLuminaire
Total
load, kW
Minimum
mounting
height, ft
…a
235
137
85
59
120
110
90
70
60
quantities based on field and stadium dimensions.
Lamps
1500-W metal halide
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DIVISION TEN
253. Basketball: Indoor
If ceiling is lower than 20 ft, more units on closer spacing should be used and recessed in
the ceiling if possible. Luminaires should be rigidly mounted, and lamps should be protected from the ball.
Spacing, ft
Class
Fixture
Lamp watts
A
B
14.2
15.9
26.0
16.8
21.0
28.0
17.0
17.0
17.5
16.0
16.0
19.2
Metal halide
College or pro
High school
Recreational
High-bay industrial
High-bay industrial
High-bay industrial
250
175
175
High-pressure sodium
College or pro
High school
Recreational
High-bay industrial
High-bay industrial
High-bay industrial
250
150
70
Mounting height
On ceiling
254. Basketball: Outdoor
Wide-beam floodlights are required to illuminate the ball when it is a considerable distance
above the court.
Floodlights
Class
Type
Recreational
65
65
Group No. per pole Total no.
B
B
2
2
Mounting height
Poles
8
8
Total load,
kW
Lamp type
3.6
2.5
400-W metal halide
250-W HPS
30 ft above court
Four per court
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ELECTRIC LIGHTING
ELECTRIC LIGHTING
10.167
255. Billiards
In large commercial parlors where a number of tables are installed, general illumination of
high intensity proves more satisfactory than individual luminaires over each table.
Equipment
Lamps
Load
Mounting height
Tournament: two two-lamp
fluorescent fixtures with
louvers
Recreational: one two-lamp
fluorescent fixture with louvers
40-WT-12 fluorescent
200 or 100 W
7 ft above floor
256. Bowling
Luminaires should be shielded by false ceiling beams or baffles unless they are of the asymmetric type. They should be positioned so as to provide even illumination along the alley
with higher intensity on the pins. Behind the foul line any type of general area-lighting
equipment may be employed.
Equipment
Lamp
Mounting height
Four two-lamp 40-W direct fluorescent fixtures per pair of alleys
One 20-W fluorescent unit per alley over the pins
40-W T-12 fluorescent
20-W T-12 fluorescent
9 ft minimum
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ELECTRIC LIGHTING
10.168
DIVISION TEN
257. Boxing
The class of bout will determine the level of illumination.
Floodlights
Class
Championship
Professional
Amateur
Type
Group
No. per pole
Total no.
Lamp watts
Total load, kW
5
5
6
A
A
A
2
1
2
8
4
8
1000
1000
400
8.7
4.3
3.6
Lamps
Mounting height
Metal halide
20 to 25 ft above ring
258. Croquet
Floodlights
Class
Type
Group
No. per pole
Total no.
Lamp
watts
Total load,
kW
Lamp
type
Tournament
65
65
65
65
D
D
D
D
1
1
1
1
4
4
4
4
250
250
175
100
1.2
1.2
0.8
0.5
Metal halide
HPS
Metal halide
HPS
Recreational
Lamps
Mounting height
Poles
Metal halide or high-pressure sodium
20 to 25 ft above court
Four per court
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ELECTRIC LIGHTING
10.169
ELECTRIC LIGHTING
259. Football
The distance between the farthest row of spectators and the nearest sideline (see table)
determines the lighting requirements, but the seating capacity should also be considered.
Either of the pole plans shown or any intermediate longitudinal spacing is considered good
practice. Local conditions determine the exact pole locations.
Class
Recommended
footcandles
I
100
II
50
III
IV
30
20
Floodlights
Distance—
poles to
sideline, ft
No. of
poles
Type
Group
No. per
pole
Total
no.
Total load,
kW
Over 140
100–140
75–100
50–75
30–50
15–30
6
6
6
6
6
8
2
2
2
3
3, 4, 5
4
A
A
A
A
A
A
24
22
12
10
6A, 8B
3
144
132
72
60
40
24
234
222
117
98
65
39
Class
Distance farthest
spectators to field, ft
Seating
capacity
I
II
III
IV
Over 100
50–100
30–50
Under 30
Over 30,000
10,000–30,000
5,000–10,000
5,000
Lamps
1500-W metal halide
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ELECTRIC LIGHTING
10.170
DIVISION TEN
260. Golf Driving Range
The floodlights should be directed so as to provide illumination on the ball throughout its
flight.
Floodlights
Aiming point
Type
Group
No. per pole
Lamp
Load per pole, kW
X
Y
Z
5
2
2
B
A
A
1
2
1
1000-W metal halide
1000-W metal halide
1000-W metal halide
1.1
2.2
1.1
Mounting height
Poles
25 to 30 ft above tees
One for every 50 ft of range width; minimum: two poles
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ELECTRIC LIGHTING
10.171
ELECTRIC LIGHTING
261. Handball: Outdoor
Glare is largely eliminated by locating the floodlights behind the players.
Floodlights
No. per pole
Class
Type
Group
X
Y
Total no.
Lamp watts
Total load, kW
Club
Recreational
65
65
D
D
1
…
1
1
3
2
1500
1500
4.5
3.0
Lamps
Mounting heigh
Poles
1500-W tungsten-halogen
At least 25 ft above court
For club play, three per pair of courts
For recreational play, two per pair of courts
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ELECTRIC LIGHTING
10.172
DIVISION TEN
262. Horseshoe Pitching
Floodlights should be directed across courts to prevent direct glare.
Floodlights
No. of
courts
Class
Tournament
4–6
1–3
4–6
1–3
Recreational
No. per pole
Type Group
X
Y
65
65
65
65
1
…
1
…
1
1
1
1
B
B
B
B
Lamps
Mounting height
Poles
Total Lamp
no. watts
4
2
4
2
400
400
250
250
Total load,
kW
Lamp
type
1.84
0.92
1.24
0.62
Metal halide
Metal halide
HPS
HPS
Metal halide or high-pressure sodium
At least 20 ft above court
Four for 4–6 court layout, two for 1–3 court layout
263. Ice Skating: Outdoor
The design suggested produces satisfactory illumination for recreational skating.
Floodlights
Area
Type
Group
W/ft2
Lamp type
Rink
65
65
65
65
B
B
B
B
0.10
0.16
0.02
0.03
HPS
Metal halide
HPS
Metal halide
Pond
The size of the area determines the number and wattage of the floodlights.
Lamps
High-pressure sodium or metal halide
Mounting height
At least 20 ft above ice
Pole spacing
Not to exceed 4 times mounting height
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ELECTRIC LIGHTING
10.173
ELECTRIC LIGHTING
264. Racetracks
The lighting equipment should be so positioned and directed as to keep glare and shadows
at a minimum.
Floodlights
Types A and B
Lamps
Load
Mounting data
Metal halide
Varies with track size
50 to 80 ft high and 50 ft inside inner edge of track
265. Shuffleboard
Floodlights should be directed across the court to prevent glare.
Floodlights
No. per pole
Class
Tournament
Recreational
No. of
courts
Type
Group
X
Y
Total
no.
4–6
1–3
4–6
1–3
65
65
65
65
D
D
D
D
1
…
1
…
1
1
1
1
4
2
4
2
Lamps
Mounting height
Poles
Lamp Total load,
watts
kW
400
400
250
250
1.84
0.92
1.24
0.62
Lamp
type
Metal halide
Metal halide
HPS
HPS
Metal halide or high-pressure sodium
At least 20 ft above court
Four for 4–6 court layout, two for 1–3 court layout
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ELECTRIC LIGHTING
10.174
DIVISION TEN
266. Skeet Shooting
Floodlights
Location
Group
Type
No per
pole
Total no.
Mounting
height, ft
Lamp
watts
Total
load, kW
B
65
2
4
25
1000
4.3
A
Lamps
1000-W metal halide
267. Soccer
For larger or smaller fields, the number of floodlights and the pole spacings should be
altered in proportion to the area of the field.
Floodlights
Class
Professional and college
High school
Recreational
Distance poles
to sideline, ft
No. of
poles
Type
Group
No. per
pole
Over 140
100–140
75–100
30–50
15–30
15–30
6
6
6
6
6
8
2
2
2
3
5
65
A
A
A
A
A
B
24
23
20
7
3
2
Total Total load,
no.
kW
144
138
120
42
18
16
232
222
193
68.7
29.4
17.3a
a
1000-W metal halide.
Lamps
1500-W metal halide
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ELECTRIC LIGHTING
10.175
ELECTRIC LIGHTING
268. Softball: Professional and Industrial League
The distance to the poles in the outfield is determined by the size of the field.
Minimum
mounting
height, ft
Group A floodlights
No. per pole
Class
Pro and championship
Semipro
Industrial League
Poles
Poles
Outfield
distance
D, ft
A’s
B’s
C’s
280
240
280
280
240
4
4
3
2
2
8
6
4
4
3
4
3
3
2
2
Lamps
Total load,
Total no.
kW
40
32
26
20
18
65.2
52.2
42.4
32.6
29.3
1–4
5–8
50
50
40
35
35
60
55
55
50
45
1500-W metal halide
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ELECTRIC LIGHTING
10.176
DIVISION TEN
269. Softball: Recreational
Layout for Type 4 or 5
Group A floodlights
No. per pole
Class
Outfield
distance
D, ft
A’s
B’s
Recreational
200
2
3
Minimum
mounting
height, ft
No. per pole
Poles
Lamps
Layout for Type 6 5
Group B floodlights
Poles
C’s
Total
no.
A’s
B’s
C’s
3
16
3
3
3
Poles
Total
no.
A’s &
B’s
C’s
18
35
40
1000-W metal halide
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ELECTRIC LIGHTING
10.177
ELECTRIC LIGHTING
270. Swimming Pool: Underwater Floodlights
Especially designed equipment is mounted in niches in the walls of the pool.
W/ft2
Location of pool
Good practice
Minimum
Outdoors
Indoors
0.5
2.0
0.3
1.6
Lamp watts
B maximum ft,
where D is over 5 ft
B’ maximum ft,
where D is less than 5 ft
E in below waterline
4
5
18–24
250–400
Lamps
Metal halide
Consult fixture manufacturer if 12.
V units are to be used.
271. Swimming Pool: Overhead Floodlights
The number of floodlights and the lamp size are determined by the size of the area and the
type of equipment.
Floodlights
Lamps
Load
Mounting height
Pole spacing
Type 6 5, Group B
Metal halide or high-pressure sodium
0.32 W/ft2 for metal halide, 0.20 W/ft2 for HPS
(Both pool and surrounding area to be lighted)
At least 20 ft above water
Not to exceed 4 times mounting height
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ELECTRIC LIGHTING
10.178
DIVISION TEN
272. Tennis: Single Court
Floodlights must be directed sufficiently high to provide even illumination on the ball during
flight.
Floodlights
No. per pole
Class
No. of
poles
Type
Group
X
Y
Total no.
Lamp
watts
Total
load, kW
Tournament
Club
Recreational
6
6
4
5
5
5
A
A
A
2
2
…
2
1
1
12
8
4
1000
1000
1000
13.1
8.7
4.4
Lamps
Mounting height
1000-W metal halide
30 ft above court
273. Tennis: Two Courts
Floodlights must be directed sufficiently high to provide even illumination on the ball during flight.
Floodlights
No. per Pole
Class
No. of
poles
Type
Group
X
Y
Total no.
Total load,
kW
Club
Recreational
6
6
5
65
A
B
2
1
2
1
12
6
13
6.5
Lamps
Mounting height
1000-W metal halide
35 to 40 ft above the court
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ELECTRIC LIGHTING
10.179
ELECTRIC LIGHTING
274. Table Tennis
When louvered fluorescent luminaires are used, they may be mounted either lengthwise or
crosswise of the table.
Fixtures
Class
No.
Type
Lamp
watts
Total load,
kW
Recreational
2
2 or 4a
Fluorescent
Deep-bowlb
40
150
0.16
0.3 or 0.6
a
For skilled play four luminaires mounted 41/2 to 6 ft above the table should be used.
Louvered fluorescent luminaires for two 40-W lamps may also be used.
b
Lamps
40-W T-12 fluorescent
150-W incandescent
275. Trapshooting
Uniform illumination will prevent apparent variation in bird speed.
Floodlights
Lamps
Load
Mounting height
Poles
Four 6 5, Group B
1000-W metal halide
4.3 kW
20 ft above ground
Two
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ELECTRIC LIGHTING
10.180
DIVISION TEN
276. Volleyball: Outdoor
Wide-beam floodlights are necessary to provide uniform illumination.
Floodlights
Class
Type
Group
No. per
pole
Total no.
Total load,
kW
Lamp type
Tournament
65
65
65
65
B
B
B
B
3
3
2
2
6
6
4
4
2.7
2.8
1.8
1.2
400-W metal halide
400-W HPS
400-W metal halide
250-WHPS
Recreational
Mounting height
Poles
20 to 25 ft above court
Two per court
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