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Q & A: The color brown

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Q:
I know what a primary colour is and I know what a completmentary colour is but what would you call brown?
- Dryden (age 6)
Northridge Public, London, Ontario, Canada
A:
Brown is a mixture of the different primary colors. The primary colors of light are red, green, and blue, which match up with the red, green, and blue-sensitve cone cells in the retinas of our eyes. Since we only have thee kinds of color-sensitive cells, you can make any color of light (at least as it appears to us) with mixtures of just the three primary colors.

I tried this with my computer monitor, running an application which lets me dial in the strengths of the red, green, and blue components, until I got something that looked rather brown to me. Here are my mixture numbers:

Red: 164
Green: 84
Blue: 30

(255 is the maximum for each of these numbers in my program -- red=255, green=255, and blue=255 is the brightest white my monitor can make). My favorite shade of brown is rather dark and is mostly red, with a bit more green than blue light mixed in.

Technical note: the spectrum of light coming from a brown object like a tree or some mud will contain all the frequencies of light in the visible spectrum, with different strengths for each frequency. You can examine this with a prism. But this broad spectrum of light is indistinguishable to our eyes from light which contains only red, green, and blue light in the appropriate mixture. If you were to look at mixtures of perfecty red, green, and blue light through a prism, you would get three sharp lines. The colors of mud and trees will give a rainbow pattern which is brigher towards red end and dimmer towards the blue end.

Tom

(republished on 07/27/06)

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