Date: Wed Oct 22 20:39:53 2008

Author: Richard Berg

Subject: Re: New member of PIRA seeks some advice... (fwd) and

Post:

Dick,

The procedure that you are suggesting IS additive color mixing. The
problem is that you are using the wrong primary colors. You would in fact
get various color mixes, but they would be hard to decipher and explain.
The important thing about choosing red, green and blue as the additive
primaries is that they can be produced as very narrow bands and they are
at the extremes of the chromaticity diagram.

For example, cyan is white with the red removed, magenta is white with the
green removed, and yellow is white with the blue removed. So shining the
cyan and the magenta filters on the same spot would produce white with
some red and some green removed, or a very washed out blue. Shining the
magenta and the yellow filters on the same spot would produce very washed
out red color.

If you use spectral yellow and cyan this would be different, but there is
no such thing as spectral magenta.

You might review some of the demos in our COLOR indes:
http://www.physics.umd.edu/lecdem/services/demos/demosn3/demosn3.htm

We do have a demo of color mixing using dichroic lights,
http://www.physics.umd.edu/lecdem/services/demos/demosn3/n3-03.htm

but as I recall they create broad band colors and it is not nearly as
effective as high quality strictly additive filters. According to the
Wikipedia these filters should have fairly narrow spectra and therefore be
good in an additive process, but my experience is that they don't work as
well.

Dick


On Wed, 22 Oct 2008, Richard Heckathorn wrote:

> Greetings,
>
> I meant shining light through each of the filters,
> cyan, magenta, and yellow and reflecting them back
> on each other. Would that not be adding colors?
>
> Dick H
>
>
> Helping teachers who facilitate, motivating
> students who learn.
> Dick Heckathorn 14665 Pawnee Trail Middleburg
> Hts, OH 44130 440-826-0834
> http://web.cvcaroyals.org/~rheckathorn/
> Adjunct Physics Teacher - Baldwin Wallace College
> Physics is learning how to communicate with ones
> environment so that it will talk back.
>
>
> -----Original Message-----
> From: tap-l-owner@lists.ncsu.edu
> [mailto:tap-l-owner@lists.ncsu.edu] On Behalf Of
> Richard Berg
> Sent: Wednesday, October 22, 2008 4:03 PM
> To: Tap-L
> Subject: Re: [tap-l] New member of PIRA seeks some
> advice... (fwd) and
>
> These are subtractive colors. There is not even
> such a thing as an
> "additive" magenta filter. If this works for
> color mixing of lights it is
> strictly fortuitous.
>
> Dick
>
> On Wed, 22 Oct 2008, Miglus, Vacek wrote:
>
>> On 10/22/08 3:05 PM, "Richard Heckathorn"
> wrote:
>>
>>> Question?
>>>
>>> What colors do you get by combining Yellow
> #104, Magenta #128 and Cyan
>>> #116 Ignore filter names, just use the
> numbers
>>>
>>> Enjoy
>>>
>>
>> Subtractive or additive combinations?
>> :-)
>>
>> Vacek
>>
>>
>>
>
> **************************************************
> *********************
> Dr. Richard E. Berg, Professor of the Practice
> Director, Physics Lecture-Demonstration Facility
> U.S. mail address:
> Department of Physics
> University of Maryland
> College Park, MD 20742-4111
> Phone: (301) 405-5994
> FAX: (301) 314-9525
> e-mail reberg@umd.edu
> www.physics.umd.edu/lecdem
> **************************************************
> *********************
>
>
>
>

***********************************************************************
Dr. Richard E. Berg, Professor of the Practice
Director, Physics Lecture-Demonstration Facility
U.S. mail address:
Department of Physics
University of Maryland
College Park, MD 20742-4111
Phone: (301) 405-5994
FAX: (301) 314-9525
e-mail reberg@umd.edu
www.physics.umd.edu/lecdem
***********************************************************************


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