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Re: color orange

From: Leonard R. Kasday <kasday@acm.org>
Date: Fri, 27 Aug 1999 13:31:05 -0400
Message-Id: <>
To: <w3c-wai-ig@w3.org>
We should really take further discussions about color per se offline, but I
just need to clear up one thing, whether colors from crt's are additive or
subtractive.  People more interested in web accessibility than the physics
of light perception may want to skip this email.

At least one person, probably more, interpreted me to say that light from
CRT's was subtractive.  Sorry, I wasn't clear there.

Actually, the light from current commercial computer displays gives
additive color mixture. This is because displays have red, blue, and green
dots.  They are so small that  your eye blends and thus adds the light from
them together so their effects are additive, just like light from the
colored slits in Jonathan's example are additive.

At least, that's how physicists like to talk about it.  From other
viewpoints you might call it subtractive, but not within earshot of any

This has diverged from web accessibility so any more discussions about this
aspect of color ought to go offline.  Of course, dicussions of color
relvant to access should continue, e.g. the color test underway at the ATRC
 http://snow.utoronto.ca/readtest/ .

Leonard R. Kasday, Ph.D.
Universal Design Engineer, Institute on Disabilities/UAP, and
Adjunct Professor, Electrical Engineering
Temple University

Ritter Hall Annex, Room 423, Philadelphia, PA 19122
(215) 204-2247 (voice)
(800) 750-7428 (TTY)
Received on Friday, 27 August 1999 13:28:11 UTC

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