Color with Pigment v. Light (Richard Hanley)

Principle(s) Illustrated

1. Visible Light Spectrum

2. Color Mixing Options with Pigment

3. Color Mixing Options with Light

Life Science Standards

6a. Students know visible light is a small band within a very broad electromagnetic spectrum.

b. Students know that for an object to be seen, light emitted by or scattered from it must be detected by the eye.

e. Students know that white light is a mixture of many wavelengths (colors) and that retinal cells react differently to different wavelengths.

f. Students know light can be reflected, refracted, transmitted, and absorbed by matter.

7a. Select and use appropriate tools and technology (including calculators, comput­ers, balances, spring scales, microscopes, and binoculars) to perform tests, collect data, and display data.

Physics Standards

4e. Students know radio waves, light, and X-rays are different wavelength bands in the spectrum of electromagnetic waves whose speed in a vacuum is approxi­mately 300,000 m/s (186,000 miles/second).

Earth Science Standards

2f.* Students know the evidence indicating that the color, brightness, and evolution of a star are determined by a balance between gravitational collapse and nuclear fusion.

4b. Students know the fate of incoming solar radiation in terms of reflection, absorption, and photosynthesis.

Questioning Script

Materials

- colored gels for lighting or opaque light paddles

Prior knowledge & experience:

Students should have some idea that mixing the colors red, yellow and blue (the primary colors) will give you all of the other colors on the color wheel.

Root question:

How is color with pigment (crayons, food dye, paints, etc.) different than color with light?

Target response:

Students will see that there is a difference between the two and infer how plants use only some the light spectrum for photosynthesis.

Common Misconceptions: There is no difference between mixing colors with pigment and mixing colors with light.

Allow students to either share their ideas about mixing primary colors to get other colors on the color wheel or use crayons, paint, or food coloring to do the same (either with students or as a demonstration). For example, if you mix:

red and yellow = orange

blue and yellow = green

blue and red = purple

green and red = brown

red, blue & yellow = black

However, if you begin to pass light through opaque but colored lenses, the story changes a bit. For example, if you mix:

blue and red = magenta

green and red = yellow

red, blue & green = white

See Fig. 3