As you probably know... a given color of light can generally, be described by one number (e.g., the frequency of its wave length).

The color white, however, has no associated frequency; it is composed of equal amounts of all the (visible) frequencies of light. Black, of course, is the absence of light. And various shades of grey are generally composed of various intensities of white (as you lower the overall intensity of white, the grey gets darker and approaches black).

The question is: why is light (optically) additive? More specifically, why is it that when we add Red and Green together we get Yellow; Green and Blue together, we get Cyan; Red, Green, and Blue together, we get white?

(Please don't confuse this with the subtractive quality of pigments/paints, where as we add more colors, particularly more of the primary colors red, yellow, and blue, we approach black.)

Could we use three (or more) different colors and achieve the same result?

The way we see the colour wheel with red, blue and green is exactly the same way that the r g b receptors in our retinas perceive light. However, we can indeed use different colours to achieve approximate results of cyan, magenta and yellow (but they will not be exactly the same, because of the way our retinas perceive the light). Light can be additive or subtractive, so we can get the various colours by mixing spectral light in varying combinations no? For instance, we see Yellow when Red and Green are optically mixed by being placed close together or are being presented together in rapid succession.  It simply depends on the mixture/combinations or the succession in which the colours are being presented.

Posted by Jane Doe on 2004-03-04 15:53:57