Re: Saga of a Novice Part 1 - LED vs Halogen

On Aug 29, 11:44 am, UKOncol...@xxxxxxx wrote:
On 29 Aug, 17:42, Richard J Kinch <ki...@xxxxxxxxxxx> wrote:

Rob writes:
But there seems to be another problem with LED's. Spectrum.

Common white LEDs are actually fluorescent lamps, and have all the spectral
problems of that type of emitter.

I think not. LEDs are quantum devices that work by electron-hole
interaction. The light quality depends on the dopant(s) in the
semiconductor junction(s), amongst other things.

Actually, both you and Richard are correct. White LEDs are InGaN-based
blue LEDs with a yellow phosphor coating made of cerium-doped yttrium
aluminum garnet. The blue light emitted by the LED is converted to a
spectrum centered at around 580 nm by the phosphor coating in a
similar mechanism that occurs in a fluorescent lamp. The blue and
yellow light combine to give the effect of a white light.

The spectrum has a sharp peak at 465 nm (due to the blue LED) and a
broad peak at 500-700 nm (due to the coating), not too unlike that of
a fluorescent lamp.

.

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