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[Physltest] [Phys-L] Re: Color (was LED mini-flashlight price break)



Mike, I think the controversy here is one of semantics, not physics. Let me define clearly what I mean by "blue" when discussing color in this thread. I argue that blue paint is blue, not cyan, because I know blue when I see blue. By "blue" I mean a color that most people agree is blue. To me, most blue-greens do not qualify as "cyan." By "cyan" I mean a color that most people agree is the same color as the cyan ink in their ink-jet printers.

Most paints and color filters reflect or transmit a large range of wavelengths. The reason why yellow and blue paint mix to produce green is that when the wavelength distribution for the yellow paint adds to the wavelength distribution of the blue paint (in the correct proportions, of course), the result is a paint that has a spectrum that peaks, averages, or just plain looks to be green in a way that most people describe as "green."

In physics, colors are defined in terms of narrow ranges of wavelengths in the visible electromagnetic spectrum. These colors are easily understood and well behaved, in the physics sense. In life and art, color is not so simple. I am not about to tell an artist that yellow and blue don't make green, because artists do it all the time. Whether the resulting "green" actually contains any of the wavelengths in the range of the electromagnetic spectrum that is usually associated with "green" is irrelevant to whether the mixed paint should be called "green". If it looks green, it's green.

Vickie Frohne

-----Original Message-----
From: Forum for Physics Educators [mailto:PHYS-L@list1.ucc.nau.edu]On
Behalf Of Edmiston, Mike
Sent: Friday, January 28, 2005 4:19 PM
To: PHYS-L@LISTS.NAU.EDU
Subject: Color (was LED mini-flashlight price break)


I am bothered by some of the things Vickie Frohne has said.

She said, "RYB works very nicely for kindergarten paints and food dyes.
These paints and dyes ARE red and blue, NOT mis-named magenta or cyan.
Kids and cooks easily make orange with RY, green with YB, and purple
with RB."

I disagree. I believe if you mix "blue and yellow" paint and end up
with green, the paint you used was not blue, but was a blue-green mix,
i.e. cyan.
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