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Light and Color1
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The sun and most light sources we are familiar with in
everyday life produce white light. Yet, we also see
colored lights, for example, in fountains, at dances, in
theaters, etc. Is colored light completely different from
white light, or are they connected in some way?
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Many interesting color lighting effects, especially those
in live theatrical productions, depend on the use of
transparent colored plastic materials called gels or
stained glass. How do these gels/stained glass and cause
the colors that they do?
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Most colored objects we see around us, however, are opaque (not transparent). So
how do we see them?
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In the following activities, we will investigate the relationship between light and color.
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Physical Sciences Connection: Develop a model to describe that light reflecting from
objects and entering the eye allows the object to be seen (4-PS4-2).
Activity 1: Color Gels
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What you will need:
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Flashlight
red, blue, green color gels
Initial thoughts: You should have red, green and blue color gels at your table, along with a light
source. Turn on the light and look through each color gel at the light source.
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Looking through a gel should make the source appear colored. Why does this happen? What
does the color gel do to the light?
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Some of the material here is taken from Physics and Everyday thinking by Fred Goldberg.
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Consider the following conversation between three students who are trying to explain what the
red gel is doing to the light.
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Anna: The gel is adding its color to the white light, making it red.
David: No, the red gel is taking away some color from the white light,
leaving it red.
Jane: No, the red gel is taking away some color from the white light,
leaving it red.
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Do you agree with Anna, David, or Jane? Do you have different idea?
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Part 1: What does each person see?
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What you will need:
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spectral glasses
color gels
flashlight/light source
Look at the white light source through your spectral glasses. You should see many bands of
colors. Concentrate on the band that spreads out to the left from the light source. The range of
colors that you see is called the color spectrum of the white light source.
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To make things simple, we can label the major color bands: Red, Orange, Yellow, Green, Blue,
Indigo, and Violet. These bands are not of equal width. For example, the red band is about the
2
same width as the green band, but each is much wider than the yellow band. The spectrum are
sometimes simply referred to as ROYGBIV.
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Close one eye and hold the red gel in front of the other eye. By moving the gel down so that it
covers only the lower half of the frame in the spectral glasses, you should be able to see the full
spectrum at the top, and the spectrum seen through the red gel at the bottom. This should help
you compare what happens to the light with and without the gel.
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What colors do you see through the red color gel?
Shade in those colors.
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What colors do you see through the blue color gel?
Shade in those colors.
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What colors do you see through the green color
gel? Shade in those colors.
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Does a gel seem to add its color to the light, take away some of the color, or both add and take
away?
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Part 2: How does light interact with a colored object?
What you will need:
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Red, green and white pieces of cardboard
sheet of white paper
flashlight/light source
The room should be dark for this part.
Stand the flashlight upright on one edge of the white
paper, and hold the red card as shown. While
looking at the white paper, move the red card in and
out of the flashlight beam while looking at the white
paper.
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What do you see on the white paper. Does the
illumination on the white paper have a particular
color?
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Repeat this for the green and white cards.
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Part 3: What happens to the other colors?
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When white light illuminates a colored object, only certain colors are reflected off of that
object. The color that is reflected is the exact same color that the object appears to have!
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What happened to the other colors not reflected? Was this light absorbed?
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To help answer these questions, students in another class performed the following experiment.
Thermometers were inserted into small pockets of white, green, red and black felt material.
These were all placed the same distance beneath a bulb, as shown in the figure. The four pockets
were all made of the same felt material, and differed only in color. After the temperatures of the
four thermometers were recorded, the bulb was turned on for five minutes.
Then the
temperatures of the four thermometers were recorded again. The data shown in the following
table represents the class averages.
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How do the increases in temperature of the red and green materials compare with the increases in
temperature of the white and black materials?
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Color
Starting
Temperature
Final
Temperature
White
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25
Green
23
32
Red
23
33
Black
23
36
Increase in
Temperature
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If we assume that the black material absorbs essentially all of the white light energy reaching it
from the light bulb, what might you conclude about the red and green materials? Would you
infer that they also absorb all of the white light energy reaching them, some of the energy, or
none of the energy? Why do you think so?
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If you thought that the colored material absorbed just some of the light energy, what happened to
the rest of the light energy that was transferred to it from the source?
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Summarizing Questions
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1. White light hits a green piece of paper. What color is reflected?
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Complete the following (color light ray) diagram. To help with this,
think about how the person is able to see the green paper.
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2. Write an explanation for why, on a hot summer day, it is more comfortable to wear white (or
very light) clothing rather than black (or very dark) clothing.
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