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4-in-1 Light Source
(OS-8517A)
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Ray Optics Kit
(OS-8516A)
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Purpose:
Determine what colors result from adding various primary colors of light. Explore the effects of illuminating different objects with different colors of light.
Background Information:
Objects that we see can be broadly grouped into two categories: luminous and illuminated. Luminous objects such as the sun generate their own light -- in the case of the sun and other stars, the light is a result of nuclear reactions taking place within the sun. The vast majority of objects we see, however, are illuminated -- that is, they are capable of reflecting light rays to our eyes, but do not generate these light rays themselves.
The colors that we see depend on the wavelength and frequency of light energy that the object reflects to our eyes. The lowest frequency humans perceive appears as red (650-750 nm wavelength), and the highest frequency appears violet
(390-430 nm wavelength). Within this range is the traditional grouping of the colors of the rainbow ("Roy G. Biv"): red, orange, yellow, green, blue, indigo and violet. Most objects reflect only part of the light spectrum: a yellow pencil reflects the yellow part of the visible spectrum only. Scientists still do not fully understand how the molecular structure of objects causes them to be able to reflect only certain frequencies of visible light.
Hypothesize: If sunlight is reflected from so many objects in so many different ways, what colors of light could sunlight be made of? Can you devise a simple experiment to test your answer? In the activity that follows, you will be asked to predict the results of combining various colors of light, and you will get a chance to see how objects' appearances change in different colors of light.
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Equipment & Supplies:
For each lab group:
- 4-in-1 Light Source: OS-8517A
- Ray Optics Kit: OS-8516A, or one convex lens per lab group
- Colored construction paper: red, yellow, green, blue
- Optional: additional colors of construction paper or additional colored objects
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Experimental Procedure:
- Place the Light Source Box on a white sheet of paper on the lab table. Adjust the box so the three primary colors (red, green and blue) are showing. It may be helpful to raise the front end of the box by approximately 1 cm so that the colored rays shine out a further distance. (Note that the concave lens from the Ray Optics Kit can be used to raise the box.)
- What color will result when the red, green and blue lights combine? Write your prediction in a Data Table like the one below.
- Place the convex lens near the ray box so that it focuses the light rays, causing them to cross each other at the focal point. What is the color of the light where the three rays come together? Record the result in your Data Table. (It may be helpful to crease the paper so it forms a "wall" upon which the focal point is projected; see Figure 1.1 below.)
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Colors Added:
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Predicted Color:
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Color That Results:
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| red + blue + green |
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| red + blue |
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| red + green |
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| green + blue |
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- Examine the Data Table and complete the "Predicted Color" column before proceeding to step 4.
- Now block the green ray with an opaque object, for example, a dark piece of construction paper. What secondary color results from adding red and blue light? Record the result in your Data Table.
- Repeat Step 5, blocking each of the primary colors in succession. Record your observations in the Data Table.
- Examine the next Data Table as shown below. Decide which colors of construction paper you will test, and fill in the first column. Then predict what color will result when each piece of paper is illuminated by red, green or blue light. Fill in the "prediction" column before proceeding.
Color of Paper
in White Light:
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Color of
Light Ray:
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Color of Paper
in Colored Light:
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Prediction: |
Results: |
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red |
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| green |
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| blue |
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red |
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| green |
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| blue |
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red |
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| green |
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| blue |
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red |
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| green |
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| blue |
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- One at a time, shine one primary color of light onto each colored sheet of construction paper. What color does each sheet of paper appear to be when illuminated by each color of light? Record your observations in the "results" column of your Data Table.
- Examine other objects in your classroom. Hypothesize what color they will appear when illuminated by colored light and then test your predictions!
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Data Analysis:
- Based on the observations you recorded in your Data Tables, describe any patterns you notice about the appearance of colored objects when they are illuminated by colored light.
- Explain how the Light Source Box "makes" red, green or blue light. (Hint: you might want to draw a simple picture to explain how each of the Light Box's filters work.)
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Conclusions and Extensions:
- You have probably used crayons, markers, or paints to mix colors and create new ones. Do you get the same results when mixing two colors of paint, say red and yellow, as you do when mixing those same two colors of light? What if you mix three colors of paint or of light? Investigate the similarities and differences between mixing colored pigments and colored light.
- Some questions related to color, light and perception remain open to scientific study. For example, does the color of light affect the way plants grow? Will certain colors affect a student's memory? Is food of a certain color more appetizing? Can color-blindness be cured? Choose a color-related question to research, and use resources on the Internet or in your school or local library to discover what scientists know about the answer to your question.
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