Xref: utzoo sci.electronics:3882 rec.audio:8418
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From: syd@dsinc.UUCP (Syd Weinstein)
Newsgroups: sci.electronics,rec.audio
Subject: Re: Looking for Blue LEDs
Keywords: blue blue blue, not yellow or red or green
Message-ID: <441@dsinc.UUCP>
Date: 23 Sep 88 15:00:06 GMT
References: <1138@nmtsun.nmt.edu> <862@ritcv.UUCP> <255@rna.UUCP> <4422@lynx.UUCP> <871@ritcv.UUCP>
Reply-To: syd@dsinc.UUCP (Syd Weinstein)
Followup-To: sci.electronics
Organization: Datacomp Systems, Inc., Huntingdon Valley, PA 19006
Lines: 43

In article <871@ritcv.UUCP> cep4478@ritcv.UUCP (Christopher E. Piggott) writes:
>Question: why are R.G.B. monitors Red, GREEN, blue, when GREEN is not one of
>the primary colors (being a combination of blue and yellow)?  Why shouldn't
>it be red, YELLOW, blue?

Its time to explain the color wheel again.  The Primary colors are
different depending on whether you are talking about light adding up
to make colors, or pigments subtracting to make colors.  The three
primary additive colors are Red, Green and Blue (suprize, RGB monitors)
The three subtractive colors are Cyan (a blue-ish green), Magenta
(A Red with some purple like tint) and Yellow.  In school you
learned to mix yellow and blue crayons to make green, the actual
primary pigment subtraction (or filtration) is yellow and cyan to make
green.  If fact, each combination of two of one set of primaries makes
one of the other.  We call that the color wheel, and if my memory
serves me correctly:


			 Red
              Yellow             Magenta

	      Green              Blue
	                 Cyan


Ok, each color is the opposite of the one diagonally across
(ie red and cyan, green and magenta, yellow and blue), and each
color is made of the two ajacent to it (read and green light makes 
yellow, magenta and cyan pigment filter white to make blue)

How it works subtractively is that Cyan does not let Red through,
Magenta does not let Green through and Yellow does not let Blue through
thus take white light and filter out the Red and Green and you have
blue left.

Totally confused?


-- 
=====================================================================
Sydney S. Weinstein, CDP, CCP
Datacomp Systems, Inc.				Voice: (215) 947-9900
{allegra,bellcore,bpa,vu-vlsi}!dsinc!syd	FAX:   (215) 938-0235