Color
Investigation
25A
25A Color
What happens when you mix different colors of light?
All the colors of visible light can be created artificially using a
combination of three primary colors: red, blue and green. In this
Investigation, you will use a white light source and color filters to
discover what happens when you mix different colors of light. You will
also learn how the filters work.
A
a.
Materials
• Optics with Light &
Color
• Colored pencils
Sources of light
Compare the light from a light bulb with the light from the same bulb when seen in a
mirror. In both cases, describe the path of the light from the source to your eyes.
b. Look at your clothes. Does the light reaching your eye from your clothes originate in your
clothes? Or does the light originate somewhere else?
c.
Turn off all the lights, and shade the windows so it is completely dark. Can you see your
clothes in the dark? What does this experiment tell you about whether your clothes give
off their own light or reflect light from somewhere else?
d. Turn on a television or computer screen in a dark room. Can you see the TV or computer
screen in the dark? What does this experiment tell you about whether the TV or computer
screen give off their own light or reflect light from somewhere else?
1
Investigation
B
25A
Color
Making colors
1. Slide all three flashlights into their own light stand.
2. Turn the flashlights on.
3. Connect the red and green flashlights by sliding their stands together using the rail
and slot connectors on the side.
4. Place the blue flashlight on top of the red and green lights, making a small pyramid
stack. Set the blue light on top of the other two with the stand on its side, so that the
rail on the stand fits in the small groove created between the stands of the red and
green lights.
2
Color
Investigation
25A
5.Set the light blue lens just in front of the lights so they
shine through it. Place the lens so the slotted side is
facing up. This will increase the visibility of the color
mixing we are looking for.
6.Set the white box that the Optics with Light & Color
kit comes in on opposite side of the paper from the
lights. Fold the top of the box over to shade the area
where the three colored lights are shining on the box.
7.Slowly move the lens away from the lights and toward
the box until you see the three spots of color (red-greenblue) overlap on the box.
C
a.
Thinking about what you observed
What color do you see when red and green light mix?
b. What color do you see when red and blue light mix?
c.
What color do you see when blue and green light mix?
d. What color is produced when all three colors of light equally mix?
Table 1: Mixing primary colors of light
Color combination
Color you see
Red + Green
Green + Blue
Blue + Red
Red + Green + Blue
3
Investigation
25A
Color
e.
Research and explain the following terms from the diagram below: cone cells, rod cells,
retina.
f.
Research and explain how the eye sees white light in terms of the photoreceptors in the
eye.
D
How does a color filter work?
A red laser can produce a single pure color of red which can be useful in some applications. For
example, making three-dimensional images, called holograms, requires a very pure source of
light which a laser can provide.
In the Optics with Light and Color kit, you have three different sources of colored light; but
just how “pure” are these colors? In this part of the Investigation you will examine the light
produced by each colored light, and learn how a color filter works. You will use the diffraction
glasses to make your observations.
1.
2.
3.
4.
4
Examine the red light with the diffraction glasses.
Using colored pencils, sketch what you see in the appropriate column of Table 2.
Repeat steps 1 and 2 for the green and blue lights.
Remove one of the color filter from one of the color lights. Examine the light produced
by the white LED and record your observations in the table.
Color
Investigation
25A
Table 2: Examining colors
Red light
Green light
Blue light
White light
5
E
a.
Drawing conclusions
Compare the colors in the red light to those in the green light. What are the similarities
and differences in the range of colors?
b. Compare the colors in the green light to those in the blue light. What are the similarities
and differences in the range of colors?
c.
How do the colors in the white light compare to the red, green, and blue lights combined?
d. The red light consists of a white LED covered with a red filter. What does the red
filter do?
e. What do color filters do?
f.
If you wanted to get yellow light, what part of the spectrum would the color filter have to
absorb?
5