Color Addition and Subtraction

"Think red and green make brown? Only with paint and crayons! In color science, those colors of light make yellow. When I demonstrate that with the Color Mixing Spotlights, students discover there's no one answer for what color a strawberry is. The demo doesn't just give them a new way of seeing color, it shows them science as a new way of seeing their world."

With the Color Mixing Projector, three seemingly simple questions give students startling answers — and all-new interest in the science of light!

What Color Is A Strawberry?
Explain that it looks red because red light is available and red light reflects back to our eyes. To confirm, shine all three colors on the strawberry. Then, shine only the green spotlight on the strawberry: it will appear black.

If A Strawberry Can Appear Black, What Color Is A Shadow?
Hold your hand in front of the red light: your shadow is black and the background red. Add the green spotlight. The red and green lights mix and the background becomes yellow creating two shadows of green and red!

Why Is The Sky Blue?
By mixing the red, green and blue light circles of the Color Mixing Projector, you will create white light. So why is the sky blue and our Sun yellow? When the white light from our Sun strikes the Earth, blue light is scattered by our atmosphere more than the other colors of the spectrum. When that happens (turn off the blue spotlight), red and green light remain and that's what produces a yellow-looking sun!


Required Equipment


Buzz Putnam

Buzz Putnam is an award-winning physics teacher and Science Department Chair at Whitesboro High School in New York. Buzz also conducts Teaching Methods classes for science teachers at Utica College of Syracuse University. In addition, he is part of the Cornell University Laboratory Development Team and a member of the Cornell NanoScale Institute for Physics Teachers.


Collin Wassilak

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