how do I give an LED a wider beam spread?

I would like to position a 5mm LED approx 3mm - 5mm behind a clear surface with a stencil in front of it. at the moment the LED projects a spot about 5 - 8mm in diameter, I'd like to make that around 20mm without changing the LED's position.
 I can replace the LED's, so if experimentation of the focal lens is required thats OK, but every time I've tried I'm made something with a dark area in the middle ;-)

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Re-design7 years ago
Scratch a clear piece of plastic with fine sand paper and put that over the led as a diffuser.  Then make a cone of alum. foil, shiny side in, so that all the led light gets projected back to your stencil.  Diffusing the led will cause some light to be lost.
frollard7 years ago
Cover the tip of the led with a spherical blob of hot glue.  Tada - scattered beam :D
Jayefuu7 years ago
Cutting the end of the LED off so it is flat instead of rounded often gives a good effect. Saw it off with a hacksaw then file it down with some medium sandpaper then fine sand paper.
lemonie7 years ago
You could find a LED with a wider angle, or use more. But another option would be to diffuse the light by roughening-up the plastic case with coarse sandpaper.

Koosie7 years ago
See if you can get a cheap, generic pair of reading glasses. They're usually available at pharmacies. Try one of the lenses in front of the LED, maybe that will do the trick.