[VAC] Re: LED Ambience and lighting.

[Dr. Gerald N. Johnson, electrical engineer]

The LEDs of the generation I've collected, perhaps 12 to 15 or 20 years
ago, have a chip mounted in a little parabolic reflector because the
light is emitted from the edges of the chip, not the surface. The shape
of the plastic serves further to focus that light. The most intense LEDs
have the most precise match of plastic and reflector to get the
narrowest beam.

I spent some time in that era, trying to make a LED project enough light
to a clay pigeon (adorned with 3m super reflective tape) equivalent to
make a quiet practice gun. The idea was to pulse the LED in the gun and
detect the reflected light from the reflective tape, if there was a hit.
With the LEDs of that era I could focus fairly decently, but was unable
to get enough light from one LED even when driven to the maximum pulse
current to detect the return reliably over more than 8 or 10 feet. I
spent a lot of LEDs in the lathe trying to improve the lens of the
package to make it smaller in diameter so the projected image could be
smaller. I failed. I could get a smaller package aperture but at great
cost in light intensity out front.

So a lens in front of the modern LED will increase the intensity at the
cost of a narrower beam but the beam may already be too narrow for
practical use without some spreading. And the external reflector may
gather some of the spilled light energy that didn't get reflected from
the chip to the package lens. For the 20 cents a lens price I saw on
some page yesterday, I'd certainly add half a dozen to a LED order from
that vendor who only sells in multiples of half dozens.

I see that the widest spread LEDs on www.ledtronics.com seem to be cut
off square instead of rounded to make a lens. And then their peak
intensity is reduced as much as 15 times the footnote says.

There's a chance this may prove to be much like hauling a Bambi with a
bicycle. E.g. it may work but not in a useful manner. Only experiment
will tell if the current generation of super brilliant white LEDs are
bright enough over a task area. Their intensity is several times that of
the LEDs I was using for the imitation shotgun. I'm sure a modern
mountain bike geared for climbing up cliffs would move the Bambi with
more ease for the rider than the standard bicycle of the 50s. But not
very fast.

Gerald J.



To unsubscribe or to change to a daily Digest, please go to
http://www.airstream.net/vaclist/listoffice.html

If replying back to this message, please delete all the unnecessary original
text from your reply.