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



Marc Kossover wrote:

[ a lot of interesting stuff ] ...

Another significant downside is the raw size of a bank
of LEDs. A bright filament is nearly a point source of
light, given the distance from the lamp to the stage.
This means that the lamps can be far away, but still
aimed precisely and even made to have defined edges.
LEDs are directional, but it takes a lot of them
side-by-side to make a bright light, and so the light
ends up being diffuse. This is sometimes an advantage,
but often isn't. There are some work arounds, but if
the light needs exact placement, LEDs don't work well.

Hmmmm. That ought to be entirely fixable.

Phase space is the key idea here. Liouville's theorem
says that the spot you make on the stage cannot be
brighter than the surface brightness of the LED chip ...
but jeepers, that's a blindingly high limit.

There are two obvious solutions (and perhaps others):

1) Make an NxN array of LEDs behind an NxN array of
lenses, so that each LED has its own lens. I figure
if the chip is 2mm on a side, a lens with a 20cm
focal length will throw a spot 2m wide 20m away.

2) Single-lens solutions:
2a) Call up the factory and tell them you want the
LED _dice_ before they have been potted into the
usual bullet-shaped plastic packages. Then bond
the chips to a suitable substrate, placing them
reeeal close together.
2b) Negotiate with the factory to have them dice
one of the wafers specially just for you, making
NxN macro-dice. This works because unlike most
lasers, the light from an LED can be taken out
perpendicular to the surface of the wafer.
http://www.acesinternational.org/Secrets_&_Tips_Fiber_Optics_(pg_3).htm
2c) Make (2a) and/or (2b) even better, and perhaps
easier to make, by coupling the LEDs to fibers
and then routing the fibers to the focal point of
the lens.

Maybe I oughtta go into business making these things.
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