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Name: Clarence L.
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 7/13/2004


Question:
I do not understand why red light+blue light makes magenta. I thought that the resultant color of 2 primary colored lights would be in between the 2 colors. For example, Take red+green, the color will be yellow. In the EM spectrum, yellow is in between red and green. So to make the color magenta, don't you need to mix the color blue with an ultraviolet light?


Replies:
Your inquiry is deceptively simple-sounding; however, you have raised a question that is far too complicated to answer in the short format available here. In fact it is an issue that has engaged (bedeviled) both artists and scientists for centuries. For example, Maxwell (of physics fame) demonstrated that color images can be created from appropriately filtered black/white images. And Newton demonstrated not only that "white" light can be de-composed into the visible spectrum, but that "white" light can be re-composed from the dispersed visible spectrum. Indeed there are many causes of color some of which do not depend upon the "mixing" of primary colors. In addition the selection of "red", "green", "yellow", "blue", "magenta", "cyan", "white", "black" is far more subtle than it appears at first sight (pun). I recommend to you a book on the subject of color entitled "Bright Earth" by Philip Ball. He traces the invention of color from its inception on the walls of caves to digital cameras. It is fascinating reading.

Vince Calder


Clarence,

The light spectrum, as seen by our eyes, is not in fact a line. It is a surface based on combinations of three primary colors. Many colors we see can be produced as a single wave: one wavelength, one frequency. Many colors we see cannot be produced this way. We have three kinds of color sensors in our eyes. This is why we have three primary colors. Ultraviolet is ultraviolet just because its frequency is higher than our sensors can notice. The color magenta stimulates both the "red cones" and the "blue cones" in your retina. A combination of red light and blue light will do exactly the same thing. As a result, a combination of red and blue light produces the same effect as magenta light. We then say that red and blue produce magenta. If we had only two kinds of color sensors, then we could describe our perception of light as a line.

Ken Mellendorf
Math, Science, Engineering
Illinois Central College



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