Hein (fub) wrote,
Hein
fub

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Diffusing LEDs

When I spoke with her last saturday, babarage confessed that even though I had dimmed the LEDs of her binary LED clock somewhat, the light was still too bright for her to sleep comfortably when the room was otherwise dark.

I had devised a plan to make two mini-LM317 power supplies, where one would supply the PIC with a voltage of 3V (the minimum operating voltage of the PIC) while the other one would supply the LEDs. The LED-supply would have an adjustable voltage (with the help of a potmeter), so that the LEDs could be dimmed.
However, when I ran such a LED on 1.5V (and hence on 5mA), it was still very, very bright. Which is good in most cases, but not in this particular case. So much for dimming the LEDs via this route.

I don't recall where I read it, but someone somewhere wrote that, if you have a LED with a waterclear lens, you can diffuse the LED's light by lightly sanding the lens. Since the lens focusses the light produced by the die (the small semi-conductor that does the actual work), sanding the lens will diffract the light, resulting in a much less focussed beam.
So I took a bit of sanding paper and set to work. After half a minute, the LED produced a very nicely diffused light -- the viewing angle is bigger, and there is no more focussed beam. And this means that there is a lot less light that bounces off the walls to keep you awake.

I might do this with future LED-clocks as well, if they are to be placed in sleeping quarters. And it's a trick I might use for other projects as well.
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