Lighting & Light Emitting Diode (LED) Lesson
Learning Goal: Define an LED. Additionally, describe how intensity, color, and
dispersion vary in LEDs. Learn how these three variables impact the amount of light at a
given distance.
Language Goal: Understand and use the following vocabulary in classroom discussion,
reading, and writing in the LED group activity.
o LED: a light-emitting diode releases light when electrons run across a
semiconductor material as voltage is applied
o Array module: several LED chips on a circuit board that are ready to be
connected to a power source
o Candella: describes LED luminous intensity; equals lumen/steradian
o Lumen: amount of luminous flux produced by a light source
o Steradian: the r2 surface area on a sphere with radius r
o Foot-candle: amount of light falling on a surface (English units)
o Lux meter: a tool used to measure the amount of foot-candles (English
units) and lux (metric units) produced by a light source
o Correlated Color Temperature (CCT): the color of a heat source in Kelvins an
LED produces
o Kelvins: unit of measure for the color of LEDs
o Cool white: approximately between 4,500 and 10,000 Kelvins
o Neutral white: approximately between 3,500 and 4,500 Kelvins
o Warm white: approximately between 2,500 and 3,000 Kelvins
o Cool colors: greens, purples, and blues
o Warm colors: reds, oranges, and yellows
o Light dispersion: redirecting light through a material (e.g. lens)
Safety
DO NOT LOOK AT THE LED DIRECTLY WHILE IT IS ON, FOR IT MAY CAUSE
TEMPORARY VISION CHANGES
Recommended Agenda:
1.
Warm-Up
a.
Brainstorm which everyday objects use LEDs
b.
Review history of light sources
c.
Define a LED and how a LED works
2.
Discuss vocabulary and read about the following topics
a.
LED light intensity
b.
LED light color
c.
LED light dispersion
3.
Divide class into small groups and gather data
a.
Vary the color of LEDs by changing array modules
b.
Vary the intensity of the LED with the pop controller
c.
Vary the amount of light dispersed by changing the lenses
d.
Measure foot-candles at different distances and record in the included
chart
4.
Post data collection
a.
Graph the results (Advanced students can extrapolate the asymptotic
equation using Excel)
b.
Answer the questions at the end of the guide
c.
Discuss resulting graphs
Light Source Timeline
o Millions of years ago: Humans used the sun and fire as a light source.
o 200+ BC: Candles invented from whale fat.
o 1880: Edison patented the light bulb
o 1961: Bob Biard and Gary Pittman patented an LED
o 1962: Nick Holonyack JR patents the first red LED using GaAsP (Gallium
Arsenide Phosphide)
o 1972: George Craford patents the first yellow LED using GaAsP
o 1972: Herbert Maruska and Jacques Pankove patent the violet LED using
Mg-doped GaN (gallium nitride) films
o 1979: Shuji Nakamura develops the first blue LED using GaN and later won
a Nobel Prize for the discovery.
What is an LED
A light-emitting diode releases light when electrons run across a semiconductor
material as voltage is applied. The following diagram shows the different components of
an LED.
LED Diagram
The way an LED works is described in the circuit diagram below. Electrons from
the n-type material fill the holes in the p-type material.
Inner Workings of an LED
Basics of LED Lighting
For LED lighting design, the three main variables are intensity, color, and
dispersion. A LED array module, like the one shown below, can look very different by
changing the three factors. Each are discussed in the following sections.
LED Array Module Shining Light on Surface
Light Intensity
Traditionally, light bulb labels describe light intensity with watts as the unit of
measure. In lighting design light intensity focuses on the amount of light on a surface or
area. The amount of light necessary depends on the type of activity performed under the
light. Guidelines like the table below give a range of desired illuminances.
Ranges of Illuminances
Type of Activity
Category
Lux
Footcandles
Public spaces with dark surroundings
A
20-30-50
2/3/2005
Simple orientation for short temporary visits
B
50-75-100
5-7,5-10
Working spakes where visual tasks are only
occasionally performed
Visual tasks of high contrast or large size
C
100-150-200
10/15/2020
D
200-300-500
20-30-50
Visual tasks of medium contrast or small size
E
500-750-1000
50-75-100
Visual tasks of low contrast or very small size
F
1000-1500-2000
100-150-200
Visual tasks of low contrasts and very small size over
a prolonged period
Very prolonged and exacting visual tasks
G
2000-3000-5000
200-300-500
H
5000-7500-10000
500-750-1000
Very special visual tasks of extrememely low contrast
and small size
I
10000-15000-20000
1000-1500-2000
General Guidelines for Foot-candle Recommendation
Each category has a recommended amount of foot-candles. A foot-candle
describes the amount light a candle projects onto 1 square foot at a distance of 1 foot.
The following illustration gives a visual representation of the definition of a foot-candle.
Foot-candle Representation
Foot-candles are the English unit of measure, and lux is the metric unit of
measure. Lux equals 1 lumen per square meter. A lux meter such as the one below
measures foot-candles and lux.
Sample Lux Meter
Light Color
The color of light produced by an LED light source is described by its correlated
color temperature (CCT) and is measured in Kelvins (K). As a reference, candlelight is
1,850 Kelvins, a standard 60-Watt incandescent is about 2,700 Kelvins, and direct
sunlight is about 4,800 K. Some LEDs can match close to a standard incandescent, while
others go towards a “bluer” color at 5,000 Kelvins as shown in the chart below. Color
choice impacts performance, appearance, mood, and efficiency.
LED Color Sample
Another impacting factor is the task performed under the lighting. Lighting color
has a proven effect on people and the tasks they perform. For example, studies show
5,500 K lighting in work settings and schools improves reading accuracy.
Color choice impacts appearance of objects in the space. Colors with reds,
oranges, and browns look better in warm lighting (2,700–3,000 K) and greens, blues,
and blacks look better in cool lighting (4,000-7,500 K). A mix of colors work best at a
natural white color between 4,000 and 5,000 K.
Color Wheel (Cool & Warm)
Also, color choice impacts people’s mood. In an intimate setting a warm color
(2,700-3,200 K) enhances an inviting environment because the color mimics the glow of
a fire. Offices and classrooms have a bright sunny feeling with cooler color temperature
(5,500-6,000 K).
Lastly, color choice impacts the efficiency of LED lighting. For example, a 2,700 K
LED gives off fewer lumens than a 5,000 K LED. Therefore, for the greatest amount of
efficiency it’s beneficial to choose a cooler color.
Light Dispersion
LED lighting loses some intensity depending on the type of lens placed in front of
the array module. A clearer material means less loss of light, therefore a clearer lens is
more efficient. Different lenses such as a smoky or prismatic lens impact the look of the
light on the desired surface.
* LED Group Activity Charts and Questions on Next Pages
Varying the color at a constant distance without lens:
Array Module
Foot-candles
Varying the intensity at a constant distance without lens:
Intensity Level
Foot-candles
Varying the light dispersion at a constant distance with same array module:
Lens
Foot-candles
Varying the distance with a chosen array module, lens, and intensity:
Distance
Foot-candles
Sample LED Lesson Questions
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1.
Where are LEDs used?
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2.
Who won the Nobel prize for inventing the blue LED?
3.
What is a foot-candle?
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4.
What tool is used to measure foot-candles?
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5.
What is the unit of measure for the color of LEDs?
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6.
What LED color range produces warm light?
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7.
What LED color range produces cool light?
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8.
Which array modules produced the highest amount of foot-candles at a
constant distance?
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9.
Which array modules produced the lowest amount of foot-candles at a
constant distance?
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10.
How many foot-candles were produced at the different intensities with a
constant distance?
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11.
12.
How many foot-candles were produced with the different lenses at a
constant distance?
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Describe your graph of distance vs. foot-candles looked like for your chosen
combination of array module, lens, and intensity.
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