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All about light and LED lighting
Teacher manual, rev. 1.1 ENG
Contents
Introduction .................................................................................... 3
A. Notes on the presentation ........................................................... 4
B. Notes on the student manual .................................................... 10
C. Answers to the exercises ........................................................... 42
D. Additional content ..................................................................... 47
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Introduction
This is the teacher manual for the Jet-Net lesson about LED
lighting. The materials for this lesson include the student
manual, teacher manual and PowerPoint presentation.
Practical lesson
You can combine this theoretical lesson with the practical lesson
"Build your own LED lamp". Students can assemble a LED lamp
from components and put it into a housing of their own design.
Prerequisites
This lesson is aimed at the second/third year of havo (higher
general secondary education) and vwo (pre-university
education). To be able to understand the material in this lesson
the students need to be familiar with concepts such as electrical
current (A), voltage (V) and power (W, kWh).
New concepts
This lesson introduces concepts such as light spectrum, colour
temperature (K), luminous flux (lm) and luminous efficacy
(lm/W).
In this manual:
This manual provides additional content to use in your lesson. It
has four sections:
A. Notes on the presentation which you can use in class, or for
other teachers
B. Material to supplement the student manual
C. Answers to the exercises
D. Links with additional material, including video clips
Teacher manual rev. 1.1 ENG, page 3
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A. Notes on the presentation
You can use the slides in the accompanying PowerPoint
presentation to support the theoretical lesson, to encourage
interaction between you and the students, and to support some
of the exercises.
Most slides do not need any explanation. Additional information
for some slides is included below. The slides are included for
reference.
1
2
3
Some natural (sun and fire) and
artificial light sources (fireworks,
chemical luminescence, stadium
lighting and a LED lamp).
The LED lamp shown here is the first
commercially available unit with a
shape similar to that of conventional
lamps and a light colour equivalent to
that of incandescent lamps.
Teacher manual rev. 1.1 ENG, page 4
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4
What are the effects of light? Are they
positive? Or negative? Where on the
earth is there most light at night? You
can see that from space. Much of that
light is due to road lighting.
5
Why is LED lighting so popular with
designers? LED lamps are small and
easy to hide. The Gallery of Honour in
the Rijksmuseum in Amsterdam is lit
with LED lamps.
6
What does lighting cost? What factors
do you consider when choosing a
lamp? Just the energy consumption?
The luminous efficacy of the lamp is
very important: the amount of light per
unit of energy.
7
The luminous efficacy is expressed as
the number of lumens per watt of
electrical energy. What is the luminous
efficacy of popular lamps such as
incandescent lamps, halogen lamps,
compact fluorescent lamp and
fluorescent tubes? Philips has
developed LED lamps with an output of
200 lumen/watt white light. These
lamps are expected to reach the
market in 2015.
8
Why were the first LED lamps oddly
yellow? LED lamps emit a cold blue
light. The yellow fluorescent layer
converts the blue light to warm white
light. When the lamp is switched on, it
provides the same warm light we are
used to from incandescent lamps.
There are now also LED lamps with a
white cover which hides the yellow cap.
Teacher manual rev. 1.1 ENG, page 5
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9
LED lamps are available in many
shapes and sizes. Each contains yellow
components which convert the light to
a different colour.
10
What is light? Visible light is only a part
of the whole electromagnetic spectrum.
The light spectrum runs from
ultraviolet to infrared, neither of which
we can see. However, most of the light
spectrum is visible to us.
11
You can make any colour light by
mixing red, green and blue light. This
principle is used in colour televisions.
They contain many red, green and blue
dots which light up. Together these
dots form the colour image.
12
Lamps emit different wavelengths.
Together these determine the colour of
the light. A low pressure sodium lamp
has a very narrow spectrum, peaking
at around 600 nm. That is yellow light.
Because they have a high luminous
efficacy (up to 200 lumen/watt) these
lamps are often used along motorways.
You can hardly distinguish colours in
this light, but visibility is good.
13
Incandescent lamps emit a broad
spectrum, with a peak in the red part
of the spectrum. All the wavelengths
together are mixed and form white
light.
LED lamps have a peak in the blue part
spectrum and as a result produce
bluish, cold light. The yellow
fluorescent cap converts this to warm
white light.
Teacher manual rev. 1.1 ENG, page 6
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14
The colour of light is indicated by its
colour temperature. We are sensitive to
the atmosphere created by light. We
experience a low colour temperature as
friendly and warm, and a high colour
temperature as remote and cold.
15
16
17
18
Teacher manual rev. 1.1 ENG, page 7
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19
Exploded view of a LED lamp.
Left to right:
Protective cover, phosphor cap, LED
chip, heat sink, electronics, base
20
Close-up of a LED chip, and LED chip
mounted on a printed circuit board
(starboard).
21
22
You can use these and the following
slides when discussing the
‘A lamp for your own room at home’
assignment.
23
Teacher manual rev. 1.1 ENG, page 8
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24
25
26
27
Teacher manual rev. 1.1 ENG, page 9
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B. Notes on the student manual
This section includes additional information to supplement
the student manual. The pages in this manual and the
student manual are numbered differently. The student
manual pages are included here for reference.
Additional content
The blue text boxes in the student manual provide additional
information, from fun facts through to theoretical background
information. It is up to you to decide if this material is mandatory or
not.
Teacher manual rev. 1.1 ENG, page 10
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The photograph on the front cover shows a LED lamp cut open. The
LED chips are clearly visible on the printed circuit board below the
protective cover. The LED chips have a typical yellow colour. This is
due to the phosphor coating which converts the blue LED light to
the warm white light we are used to from incandescent lamps. This
is explained in section 5.2. Underneath the LED chips you can see
the electronics which supply the LED chips with a stabilised low
voltage and constant current.
Teacher manual rev. 1.1 ENG, page 11
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You can use Exercise 1 to remind your students of what they know already.
Alternative questions or exercises to get going could include:
 What lamps do you use? Are you already using LED lighting at home? What
do you know about how lamps work? And about LED lamps?
 Calculate the costs of leaving a 40 W incandescent lamp, 12 W compact
fluorescent lamp and 8 W LED lamp on for 365 days. (The light output of
these lamps is similar.)
Teacher manual rev. 1.1 ENG, page 12
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Teacher manual rev. 1.1 ENG, page 13
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You could refer to the famous formula
proposed by Albert Einstein. You
can use the speed of light to calculate the amount of energy stored in a particle
of known mass.
Question: A particle of uranium in a nuclear reactor has a mass of 3.9510-25 kg.
Use the speed of light and Einstein's formula to calculate the amount contained
in the uranium particle.
Answer: E = mc2 = 3.95*10-25 * (299,792,458)2 = 3.55 *10-8 Joule
The electromagnetic spectrum is discussed in outline.
Depending on the level of your students you may decide to
discuss it in greater detail. For example, you could discuss
wavelength, frequency and spectral distribution in greater
detail.
Teacher manual rev. 1.1 ENG, page 14
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If you want you can discuss the difference between luminous
intensity and luminous flux in greater detail here.
The luminous intensity indicates how much light a source
emits per steradian (sr), the unit of solid angle. The luminous
flux is calculated by integrating the luminous intensity of light
source across the aperture of that light source.
(1 lm = 1 cd * 1).
Teacher manual rev. 1.1 ENG, page 15
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You can use an ordinary camera to demonstrate the concept of
colour temperature. On the following page we describe an
experiment which you can demonstrate or the students can do
it themselves.
Teacher manual rev. 1.1 ENG, page 16
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Experiment: determining the colour temperature
with a camera
Whether you look at a sheet of white paper under daylight
(sun) or under lamplight, you perceive it as a sheet of
white paper. That is because our brains adapt. But are you
really seeing the same colour white?
Sunlight and lamplight do not have the same colour
components: Sunlight has more blue, and lamplight more
red/yellow light. That means that the same sheet of white
paper is illuminated differently and therefore also reflects
different colours. Because you know it is the same white
sheet of paper your brains conclude that it is the same
shade of white each time. But it's not like that. The sensor
in a camera is much more honest. You can use it for an
experiment.
Experiment
 Set the camera to "Manual" and in the "Settings menu"
go to "White balance".
 Set the camera to the sun symbol.
 Now take a photograph under lamplight of the white
sheet of paper. Do NOT use flash.
 Then take a photograph WITH flash.
The two photographs are clearly different. The photograph
under lamplight is much too red and yellow compared to
the flash photograph.
What happened?
Your camera is usually set to AWB: Automatic White
Balance. With this setting the camera will look for a white
area and use that to set the colour temperature. In other
words: anything with this colour temperature will be
imaged as white.
By selecting the sun symbol, the camera's white balance is
set to 5500 K, the colour temperature of daylight.
However, the colour temperature of lamplight is around
3700 K. Because of that the white paper will look too
yellow or red. Photographic flashlight has a colour
temperature of 5500 K, it's like an artificial sun.
The reverse can also happen. If you take a picture indoors,
the colours in the room are often reproduced correctly, but
a window with light outside will be too blue. The camera
corrects the red-yellow light in the room but removes too
much red from the sunlight coming in from outside. As a
result blue dominates.
Teacher manual rev. 1.1 ENG, page 17
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Teacher manual rev. 1.1 ENG, page 18
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In this section it is assumed that the students are familiar with the
concept of efficiency. If they are not then you will have to explain it
first.
Teacher manual rev. 1.1 ENG, page 19
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Teacher manual rev. 1.1 ENG, page 24
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Visit
http://www.lighting.philips.nl/application_areas/LAC_OLAC/
interactieve-tour-lac.wpd
for a virtual tour of the Philips Lighting Application Centre.
Teacher manual rev. 1.1 ENG, page 25
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Teacher manual rev. 1.1 ENG, page 29
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The text box on this page explains in detail how a LED
chip works. This is fairly complex and only suitable for
outstanding students.
Teacher manual rev. 1.1 ENG, page 30
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Teacher manual rev. 1.1 ENG, page 36
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The discussion related to Exercise 9 covers a range of issues. Historically,
cheaper light sources have resulted in greater use of lighting (from a single
candle to a number of kerosene lamps to lighting in the garden and public
spaces). Will architects and lighting designers use more light because LED
lighting gives them greater freedom in their designs? Are people prepared to
buy more expensive lamps which are cheaper to use? Does this mean we can
leave the light on everywhere because these lamps use little energy? And what
is the impact of the longer lifetime of lamps? Will shops lose turnover and will
electrical contractors have less work?
Teacher manual rev. 1.1 ENG, page 37
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Teacher manual rev. 1.1 ENG, page 40
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Teacher manual rev. 1.1 ENG, page 41
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C. Answers to the exercises
Exercises 1 - 9
1. The students are free to give their own answers.
2. a. Yes, shining the three lamps on the same surface should
produce light which is almost white. However, it is difficult to
get this exactly right as the three lamps have to have
exactly the right wavelength.
b. The blue lamp has a wavelength of approximately 450
nm, the red lamp has a wavelength of 700 to 780 nm, and
the green lamp has a wavelength of 520 to 550 nm. White
light contains all wavelengths in the same intensities.
3. Lamp 1 is most suitable for an industrial building; it has a
high light output which means that a large area of the
building can be lit with the one lamp. The lamp also has a
high colour temperature, which means it gives white light
which is suitable for work.
Lamp 2 is more suitable for a living room; the lower
luminous flux is not a problem as the room is small, and the
lower colour temperature means the lamp gives a yellowish,
warm light.
4. The students are free to give their own answers
5. Assuming 52 weeks per year, 5 days per week, and 3 hours
per day, the lamp will burn 15 hours per week, i.e. 780
hours per year. if we divide the lifetime by the number of
hours it is used per year we get:
40,000 operating hours / 780 hour/year = 51.28 years = 51
years (rounded).
6. The students are free to give their own answers.
7. A LED lamp has many more components than a standard
incandescent lamp or compact fluorescent lamp. The
components as such are not particularly expensive, but the
combination of them and the complexity of the LED chip
means that these lamps are more expensive than
conventional lamps. With respect to the LED chip you could
mention that it contains sapphire: this is a costly material
which is essential to their operation.
8. One advantage is that the lamp emits more light, as it does
not have a cover which might reduce its output. Potential
disadvantages are that the phosphor cap has less protection
Teacher manual rev. 1.1 ENG, page 42
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or that consumers might not like a lamp which looks like this
(they might consider the yellow cap as ugly).
9. The students are free to give their own answers.
Answers to: A lamp for your own room at home
The following information on the packaging is relevant when
choosing a lamp:
Softone compact
fluorescent lamp
LED lamp
12 W
8W
610 lm
600 lm
2700 K
(warm white)
2700 K
(warm white)
no
no
60% light output
10-80 s after
switching on
100% light output
immediately after
switching on
Maximum
number of on/off
cycles
10,000 x
50,000 x
Lifetime
10,000 h
15,000 h
Energy
consumption
Luminous flux
Colour
temperature
Dimmable
Run-up time
Colour rendition
Ra > 80
Equivalent to an
incandescent
lamp of
51 W
48 W
Saving compared
with an
incandescent
lamp
(51-12)/51= 76%
(48-8)/48 = 83%
Hazardous
substances
Contains mercury
The LED lamp produces approximately 1.5% less light than the
Softone lamp. You can find the colour rendition index of the
Softone lamp on the web. It is just over 80, about the same as
that of the LED lamp. As far as the other aspects are concerned
the LED lamp is similar to or better than the compact fluorescent
lamp. The LED lamp costs more than the compact fluorescent
lamp but prices are rapidly dropping.
If you've got it at hand then the LED lamp is the obvious choice.
Teacher manual rev. 1.1 ENG, page 43
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Answers to: New lighting in the bicycle store
a) The lamps produce 20 lumen/watt and are 80 watt each.
So, per lamp: 20 lumen/watt * 80 watt = 1600 lumen.
There are 6 lamps in the basement, so the total amount of
light we need is:
6 lamps * 1600 lumen/lamp = 9600 lumen.
b) You can calculate the missing values for the power, luminous
flux and luminous efficacy using the formula in section 2.3:
.
You can find the other missing information in the text and on
the web. The result is:
Compact
fluorescent
lamp
LED lamp
Sodium lamp
Mercury
lamp
Power
(watt)
40
20
40
80
Luminous efficacy
(lumen/watt)
70
100
120
60
Luminous flux
(lumen)
2,800
2,000
4,800
4,800
Lifetime
(hours)
10,000
25,000
28,000
16,000
4.95
39.95
56.95
21.05
Harmful
Not harmful
Harmful
Harmful
Varies
Varies
Yellow/orange
Yellow
Cost
(€)
Environmental
impact
Colour temperature
c) The answer to this question depends on the choice the
students make. Two sodium lamps are the most obvious
choice.
Sodium lamps - example:
The sodium lamp has a luminous intensity of 5,600 lumen.
This means that two of these lamps are enough to get the
same luminous intensity as in the baseline case
(incandescent lamps): 11,200 lumen.
Teacher manual rev. 1.1 ENG, page 44
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The lamps will be on for 8 hours a day;
that is 40 hours per week, and 1,600 hours per year.
The lifetime of a sodium lamp is 28,000 hours. So a sodium
lamp will last 28,000 / 1,600 = 17.5 years. The cost per year
of such a lamp is 56.95 EUR / 17.5 = 3.25 EUR
Two sodium lamps will be needed.
Hence the cost will be 2 * 3.25 EUR = 6.50 EUR per year.
The same calculations for the other lamps:
Lamp
Compact
fluorescent
lamp
LED lamp
Sodium
lamp
Mercury
lamp
Quantity
needed
4
(4*2,800 =
11,200 lumen)
5
(5*2,000 =
10,000 lumen)
2
(2*4,800 =
9,600 lumen)
2
(2*4,800 =
9,600 lumen)
Lifetime
Cost per
lamp per
year
Cost per year
10,000/1,600=
6.25 years
4.95/6.25 =
0.79 EUR
4*0.79=
3.16 EUR
25,000/1,600 =
15.6 years
39.95/15.6=
2.56 EUR
5*2.56=
12.80 EUR
28,000/1,600 =
17.5 years
56.95/17.5 =
3.25 EUR
2* 3.25=
6.50 EUR
16,000/1,600 =
10 years
21.05/10=
2.10 EUR
2*2.10=
4.20 EUR
d) The answer to this question also depends on the choices the
students make. Here is the continuation of the calculations
for the sodium lamps.
Every year the two sodium lamps will be on for 1,600 hours,
that is 3,200 hours/year = 11.52 million seconds per year.
The rating of the lamps is 40 watt = 40 J/s.
The lamps use 40 Joule/s * 11,520,000 s = 460,800,000
joule, i.e. 460,800 kJ per year.
1 kWh is 3,600,000 J hence the two lamps consume:
460,800,000/3,600,000 = 128 kWh per year.
1 kWh costs EUR 0.22, hence the electricity costs per year
are: 128 kWh * 0.22 EUR/kWh = 28.16 EUR.
Alternative calculation:
Per year the operating time of two sodium lamps is 2*1,600
= 3,200 hours.
The rating of each lamp is 40 watt. So per year the two
lamps use 3.200*40=128,000 Wh = 128 kWh.
The cost of 1 kWh is 0.22 EUR.
Teacher manual rev. 1.1 ENG, page 45
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The electricity costs per year are 128*0.22 = 28.16 EUR.
The same calculations for the other lamps:
Number of
hours
Number of kWh
Electricity
costs per year
Compact
fluorescent
lamp
4*1,600 =
6,400 hours
40*6,400/1000 =
256 kWh
256*0.22 =
56.32 EUR
LED lamp
5*1,600 =
8,000 hours
20*8,000/1000 =
160 kWh
160*0.22 =
35.20 EUR
Sodium
lamp
2*1,600 =
3,200 hours
40*3,200/1000 =
128 kWh
128*0.22 =
28.16 EUR
Mercury
lamp
2*1,600 =
3,200 hours
80*3,200/1000 =
256 kWh
256*0.22 =
56.32 EUR
Lamp
e) The overall lighting costs consist of the sum of the cost of
the lamps and the electricity costs. The total costs of lighting
the basement amount to:
Using compact fluorescent lamps: 3.16 + 56.32 = 59.48
EUR per year
Using LED lamps: 12.80 + 35.20 = 48.00 EUR per year
Using sodium lamps: 6.50 + 28.16 = 34.66 EUR per year
Using mercury lamps: 4.20 + 56.32 = 60.50 EUR per year
f)
If the students consider the environmental factors, colour
temperature and sufficient number of lighting points then
LED lamps can be defended as the best choice for the
basement.
Teacher manual rev. 1.1 ENG, page 46
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D. Additional content
Lighting University
The Philips web site provides a large amount of additional
material: articles, pictures and videos.
http://www.lighting.philips.com/main/connect/Lighting_Universit
y/index.wpd.
For example there are helpful videos about difficult subjects such
as colour rendition
(http://www.lighting.philips.com/main/connect/Lighting_Universi
ty/just_in_time_learning_videos_about_lighting/colorrendering.wpd)
and colour temperature
(http://www.lighting.philips.com/main/connect/Lighting_Universi
ty/just_in_time_learning_videos_about_lighting/color_temperatu
re.wpd).
The student's programme
http://www.lighting.philips.com/main/connect/Lighting_Universit
y/student_program.wpd was developed specially for schools and
includes lessons as well as a test.
Lighting Application Centre
Go to
http://www.lighting.philips.nl/application_areas/LAC_OLAC/inter
actieve-tour-lac.wpd to pay a virtual visit to the Philips Lighting
Application Centre and learn about the different ways in which
light can be used.
Teacher manual rev. 1.1 ENG, page 47