Re: [Phys-l] Projecting Black

[Rick Tarara <rtarara@saintmarys.edu>]

I think--just looked carefully at a black spot on a computer screen--that it 
is simply that black does not illuminate any of the red, green, or blue 
pixels.  On an LCD screen, none of the pixels are activated.

Rick

----- Original Message ----- 
From: "Ron Curtin" <ron.curtin@charlottecountryday.org>
To: "'Forum for Physics Educators'" <phys-l@carnot.physics.buffalo.edu>
Sent: Tuesday, November 06, 2007 3:35 PM
Subject: [Phys-l] Projecting Black


> A student asked me a question that I couldn't answer.  When I pick up the
> black pen on my Smart Board, I can write with a really black color ---  
> much
> blacker than the appearance of the screen with no illumination at all.
> Where does the black come from?  I can produce most all the other possible
> colors with a combination of the primary colors of light, but if I add all
> the colors of light together, it seems like I should get white, not black.
> Any help?
>
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