Re: [Phys-l] About black zones in screens

[Bernard Cleyet <bernardcleyet@redshift.com>]

You mean multiplication?

bc defers to JD.

Wrong!?

4  Secondary Colors

You can demonstrate the idea of secondary colors very simply. (This doesn’t have much to do with food coloring directly, but it is fun and informative.) Get three colored LED flashlights: red, green, and blue. (They were on sale for $1.00 apiece at the drugstore, the last time I looked.) Aim all three of them at the same spot, from slightly different angles. (The easiest way is to recruit a helper to hold two of the lights.) The three colors will mix, additively, to form a fair approximation of white. Now comes the fun part: interpose something that casts a shadow. A spoon works well. You will see three main shadows, each with a different color, namely cyan, magenta, and yellow. That’s because each shadow-area is illuminated by two sources, while the spoon blocks the third.



http://www.av8n.com/imaging/dye-spectra.htm


On 2010, Nov 18, , at 10:27, Folkerts, Timothy J wrote:

> It also works very well to show color addition of the projectors -- red
> and green make yellow