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Re: [APD] If it's good for street light...

I'm not really up to date on the superbright LEDs, but I'll
share what I know.

The photon that is emitted in fluorescent bulbs is a UV
frequency, when the UV photon hits the phosphor paint it is
absorbed by an electron, which is then unstable and emits a
photon but at a lower wavelength. The wavelength is, to put
things crudely, a function of the kind of phosphor.

In the LEDs the electrons are roaming around all the
molecules in the crystal but they each still have a
specific energy level so exciting them kicks out a photon. 
In super bright LEDS, the crystal is doped and their is a
secondary emmission of a photon stimulated by the first,
sort of similar to the UV photon striking a phosphor in a
fluorescdent tube lamp except that there is no plasma
(conductive gas) involved, it's all solid state.

Unless the LED is really fancy, the output comprises
relatively small portions or spikes of the visible
spectrum. But they are broad enough to be useful. You can
put a red, green, and blue LED in combination and
reasonably white light, much the same way your TV makes you
see white.

The type of material with which the super bright LED is
doped determines whether it's a green, blue, white LED.

I believe that various colors of LEDs are possible without
the doping but most, other than the classic red, are very
low output. What made the superbrights the next big thing
is LEDs was the idea to dope the diode, to create
fluorescence in a solid state device. I'm sure what I've
said terribly oversimplifies the whole matter.

Also check out this page, especially the part of the page
called ": How do those white LEDs work anyway?":


Hope that helps,
Scott H.
--- "Mariano F. Bonfante" <mariano_bonfante at hotmail_com>

> Nice site Scott. Let me ask you about the white leds. I
> study years ago that 
> the light emission of a PN junction was related to an
> electrode coming down 
> from an excited orbit to a more stable one. In this case
> the photon released 
> has a specific wavelength related to the orbit energy
> difference.
> In this aspect, a white emission would not be possible.
> Other way to produce such spectrum is to operate a light
> emitter with 
> extremely narrow pulses, so the emitted light would be
> white.
> Do you have an idea how white leds work?.
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