Adding Colors: An Optical Experiment

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Updated on May 13, 2014

True or False? Every time you observe white, all of the colors of the spectrum are present.

Would it surprise you to learn that the answer is false? Your brain can be tricked into seeing white. This deception occurs when you view the right mix of certain colors and shades. Two-color combinations, such as blue mixed with yellow or red mixed with bluish green (called cyan), can also appear white.

Can other combinations produce the illusion of white? Let's find out.

What You Need:

  • 3 flashlights
  • transparent plastic report covers (red, blue, and green)
  • a pair of scissors
  • adhesive tape

What You Do:

  1. Cut out a disk from each report cover about the size of the flashlight lens.
  2. Tape one disk over the clear lens of each flashlight. Aim the red beam at a nearby white wall. What color do you see?
  3. While the red remains on, aim the beam of blue so that it overlaps half of the red spot. What happens?
  4. Now aim the beam of green so that all three colors fall on the same spot. What happens as the colors are added to each other?

The Science

When light beams mix, the combined colors are added together. Unlike the mixing of paint pigments, this additive process produces lighter colors. When the right combination is produced, we "see" white.

Real-World Connection

The next time you're in a performance theater, take a look at the stage lights. Most likely, you'll see a row of lights that surround the stage. These border lights aren't white. Instead, they consist of a pattern of colored lights. When projected, these different colors create white.

Reprinted with permission from "Awesome Experiments in Light and Sound" by Michael Dispezio (Sterling Books, 1999).

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