Next to the checkout stand at Walgreens they are selling
little LED flashlights for $1.00 apiece. Your choice of
-- red
-- green
-- blue
-- white
I remember when they sold for many times that price.
These are *not* lasers ... they are not collimated and
they are not monochromatic. But the colors look reasonably
intense.
They're remarkably bright for their size (2cm*2cm*.5cm),
the "bulb" will never burn out, and battery life is very
good.
They're great fun to play with. You can arrange three
primary colors in a circle, pointing inward, and make
little Venn diagram with white in the center.
Also remember, if you don't have a nice diffraction
grating handy, a CD (especially a blank CD-R) will do
the job after a fashion. (DVDs don't work.)
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