Expert: Paul Wagner - 1/31/2005

Question
What color would a red cloth be if it were illuminated by a white light, a green light, and a blue light. I need an answer for each color.

                          Thanks, Mike


Answer
Dear MIke:

This sounds suspiciously like a homework question....

For white light, the answer is pretty obvious, isn't it?  The sun is pretty close white light, and red cloth looks red in the sunlight, right?  

Why?

Because it absorbs all of the other colors of the spectrum, and reflects only the red light.  

So what happens with blue light or green light?  

What do you think?  If red cloth absorbs all light other than red, and then reflects the red back to our eyes, what will it do with green light?  If the cloth is truly pure red, and the light is purely green, then the cloth will look pretty black.  The same is true of blue light...although both will be affected by the color of the cloth and the wavelength of the colored light.  The blue light can make the red cloth look a bit purple.  Green, because it is on the opposite of the color wheel, really does look black, or very dark brown.

Paul Wagner