ELEC-E8700
Principles and Fundamentals of Lighting
II/2016-2017
Laboratory work
Lab 1 – Light and lighting measurements (indoor work place)
Aalto University, autumn 2016
ELEC-E8700 PRINCIPLES AND FUNDAMENTALS OF LIGHTING
LABORATORY WORK 1 – LIGHT AND LIGHTING MEASUREMENTS
II/2016-2017
Introduction
The laboratory work is done in groups of 2-4 persons. Each member of the group must
return his own report on the work using the course workspace in MyCourses (pdf format is
preferable). The report should be submitted within a week after the laboratory work.
Participation to laboratory exercises is one of the requirements to pass the course.
Lighting measurements
Illuminance
A conventional illuminance meter is composed of a photo-electric cell and the instrument
part. The photocell transforms light into electric current, which is proportional to the
illuminance on the surface of the cell. The resulting current is then measured, and the
result is presented on a scale calibrated to show the correct lux values. The principle of an
illuminance meter is shown below in the Fig. 2.
Fig 2: The working principle of illuminance meter
Fig 3: Illuminance meters
The spectral sensitivity of the photocell is very different from that of the human eye, which
makes the measurement results depend on the colour of the light. However, the sensor is
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ELEC-E8700 PRINCIPLES AND FUNDAMENTALS OF LIGHTING
LABORATORY WORK 1 – LIGHT AND LIGHTING MEASUREMENTS
II/2016-2017
equipped with a filter with which the colour error can be reduced or almost eliminated.
Even a good-quality illuminance meter can still suffer from significant colour errors, and
instruments made for field work can have an error of 10% or more if the colour of the light
is not taken into account.
Another source of error is caused by the incident angle of the light. This cosine error can
be as much as 25%-50% of the meter reading, unless the instrument is equipped with
sufficient cosine correction. This is accomplished by using a diffusing plate or dome over
the photocell, but even when “corrected” the cosine error can be 10%.
The temperature of the sensing part can also produce error. Usually the meter is calibrated
at normal room temperature, and the reading is accurate only if the measurement is made
on those conditions. Some cells can produce 5% error if the temperature is changed by
10oC.
Basic procedure when measuring the illuminance distribution in a room
Fig 4: An example of the measurement grid. The circles are the measurement points.
The measurement grid is defined by making a drawing of the furnished room and dividing
it into squares or rectangles so, that the each side of the square/rectangle is no more than
about 50% of the distance between the light source and the working plane. The grid must
be devised so, that the measurement points (at the center of each square) are not located
symmetrically with the luminaires (i.e. measurement points must not all be under a
luminaire). The illuminance is measured at the approximate centre of each square at the
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ELEC-E8700 PRINCIPLES AND FUNDAMENTALS OF LIGHTING
LABORATORY WORK 1 – LIGHT AND LIGHTING MEASUREMENTS
II/2016-2017
level of the working plane, and the results are written down into the drawing. The average
illuminance in the room is the average of the illuminances of the squares. In addition, the
lowest and highest illuminance is sought from the room.
Similar measurement can be made in the working place or other “interesting” places of the
room.
Important note: This basic measurement procedure should be complemented in practice
with the instructions provided in the standard standard SFS-EN 12464-1 "Light and
lighting. Lighting of work places. Part 1: Indoor work places”.
Luminance
Although the outward appearance of a luminance meter is very different from that of an
illuminance meter, the working principle is very much the same. The only difference is, that
a luminance meter is built with optics to limit the angle which the photocell sees.
Fig 5: Luminance meters
Before the measurements
1.
2.
3.
4.
5.
6.
How does an illuminance meter work? (General outline)
What is “cosine error” and how it is avoided?
How are the measurement points chosen in an illuminance measurement?
What is illuminance measurements used for?
How does a luminance meter work?
How can luminous intensity be measured?
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ELEC-E8700 PRINCIPLES AND FUNDAMENTALS OF LIGHTING
LABORATORY WORK 1 – LIGHT AND LIGHTING MEASUREMENTS
II/2016-2017
Measurements
1. Basics of illuminance and luminance meters. Estimate the illuminance or luminance
at some point at the room and check your estimation with the meters.
2. Plan the measurement of the illuminance distribution in the room and carry out the
measurement.
3. Measure illuminance on the table.
4. Measure the availability of daylight as function of distance from the window.
5. Measure the luminance of an OLED lamp and a fluorescent lamp. Measure also the
physical dimensions and note the wattages of the lamps.
6. Measure the luminance distribution in the room with the fish-eye luminance meter.
7. Estimate the reflectance of the two given surfaces. Check your estimation with the
help of an illuminance meter.
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ELEC-E8700 PRINCIPLES AND FUNDAMENTALS OF LIGHTING
LABORATORY WORK 1 – LIGHT AND LIGHTING MEASUREMENTS
II/2016-2017
Student name:
Student number:
Group:
Date of the lab work:
Report
Answer to the following questions using and presenting the original measurement results.
1. What can you conclude on the visual (i.e. without measurement instruments)
estimation of lighting quantities?
2. Present the illuminance distribution in the room by drawing isolux curves (see
example in Fig.1). Present also the average illuminance and the uniformity (Uo) of
𝐸
the lighting in the room. 𝑈𝑂 = 𝐸 𝑚𝑖𝑛
𝑎𝑣𝑒𝑟𝑎𝑔𝑒
3. Present the distribution and uniformity of illuminance on the table surface.
4. Present a figure showing how daylight behaves when the measurement point is
moved away from the window. Can you present a mathematical law for this?
5. Calculate the luminous fluxes and the luminous efficacies of the OLED and
fluorescent lamps with the help of the results of the measurement 5.
6. Present the luminance distribution measured by the fisheye-lens camera. In what
ranges do the luminances typically lie for room surfaces? Is 10 000 cd/m 2 much or
little for lamps?
7. Calculate the reflectance of the measured surface and compare it with your
estimation. What can you conclude?
8. Final conclusions, discussion and reflections.
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ELEC-E8700 PRINCIPLES AND FUNDAMENTALS OF LIGHTING
LABORATORY WORK 1 – LIGHT AND LIGHTING MEASUREMENTS
II/2016-2017
Fig 1: Isolux curves
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