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[Phys-L] Re: LED mini-flashlight price break



Larry Smith wrote:

Could they fool someone into thinking they are lasers?

Well, they won't fool anyone on this list.
But I'm sure they would fool "someone" :-)

What is the divergence of the beams?

About .1 radian. That is: spot radius about 10cm
at 1m from the source ... but the spot just sorta
fades out without sharp edges, and I'm not motivated
to measure it precisely.

Note this is about 500 times less collimated than
typical good-quality laser pointers. (I don't know
about the divergence of my dollar-store lasers; I
haven't measured them, either.)

=============

Also, lasers have a verrry narrow spectrum, while
the LED flashlights are broad. Each of the three
(R, G, B) covers about 1/3rd of the visible spectrum.

It is great fun to bounce a green laser off a
diffraction grating and compare it with a red laser.

A CD makes a plenty-good-enough grating for this
demonstration, but beware that on some CDs spacing
of the graging varies from place to place on the disk.
The variation is gradual, and not too huge, so if
you're trying to do anything quantitative, you can
solve the problem simply by marking a small "target
area" on the disk and being careful to use only that
area.