White LED's other than Blue LED + Yellow Phosphour

White LED\'s other than Blue LED + Yellow Phosphour

Why was blue + yellow chosen? Efficiency? Is there any other combinations that would result in better output or consistancy?

Think about these..: (note, you could have a X colored LED with Y phoshpur, or Y LED with X phosphur) Where X=1st color, Y=2nd color.

Green + Purple (R+B)
Red Cyan + (G+B)
UV/Blue + White(phos)
RGB(led) + White(phos) <-- Helps blend the RGB dies.

As you can see you could have a Red led with Cyan phos, or a Cyan led with red phos.. The red led would be the most effeicent probably..

Re: White LED\'s other than Blue LED + Yellow Phosphour

I know that some version of the Cadillac uses a map light composed of a blue-green LED and a yellow or amber LED to approximate white. Some LED company is making these, though I don't have any additional information about this. Maybe it's Norlux, maybe it's something else. /ubbthreads/images/graemlins/jpshakehead.gif

Re: White LED\'s other than Blue LED + Yellow Phosphour

The ideal would have been an ultraviolet LED with red, green and blue phosphors, just like the stardard fluorescent tubes, or cold cathode CCFL.

White can be also obtained with two colors only, if it is possible to control, very precisely, the wavelenght and the spectral power contents of the sources. (The principle was discovered by the US scientist Edwin Land).

Red phosphors have, for long time, been hard to produce and they are inefficient. Now they are more easy to produce, altough more expensive then green and blue. But they are still inefficient.

The blue source with yellow phosphor, like the white Nichia and white Luxeons, has a pretty good efficiency conversion, higher than an UV source with 3 phospors. This adds to the incredibly high efficiency of blue source itself, obtained with P-doped gallium. (Think of a SiC LED)

I believe it is possible to built a UV LED with three phosphors, but it, at present state of the art, would have nowhere the brightness of white Nichia or LSs nor the 100K life span.

Other combinations are not practically possible: phophors, in the range of efficiency we are interested in, can only down-convert the light coming from the source. As an example, there are no phosphors that can elevate the frequency from red to blue with reasonable efficiency.

Anthony.

Re: White LED\'s other than Blue LED + Yellow Phosphour

@Isaac - I think, the light spectrum of a red led will not charge the phosphor coating. You can try that yourself - use a red led to charge the luminous hands of your watch and you'll soon find out, that it won't work. Whereas a blue led charges the phosphor-stuff pretty well... At least, that's what I experienced.

Chris

Re: White LED\'s other than Blue LED + Yellow Phosphour

If you use a stokes phosphor and an IR LED, you can get green light. The process isn't too different from how a green laser pointer works, and it's horribly innefficient, but it *is* possible.
Back in the late 1960s, GE put out at least a couple of green LEDs that worked like this: a stokes phosphor on top of an IR LED die.

Re: White LED\'s other than Blue LED + Yellow Phosphour

Stokes or Anti-Stokes ?

[ QUOTE ]
Materials which can be excited with IR radiation to emit radiation of a higher energy in the IR or visible region of the spectrum are known as 'Anti-Stokes' or 'up-conversion' phosphors.

[/ QUOTE ]

Chris

P.S. I'm asking because I never heard about this before and a fast search brought up this page...

Re: White LED\'s other than Blue LED + Yellow Phosphour

[ QUOTE ]
ChrisA said:
Stokes or Anti-Stokes ?...

[/ QUOTE ]
Anti-stokes...my mistake. /ubbthreads/images/graemlins/blush.gif

Re: White LED\'s other than Blue LED + Yellow Phosphour

You're welcome. Not trying to be a smarta$$... /ubbthreads/images/graemlins/wink.gif

Chris

Re: White LED\'s other than Blue LED + Yellow Phosphour

Lumileds has great slides from their presentations at various conferences that explain exactly why they've chosen the Blue LED/Yellow phosphor route. Those presentations are available on their website:

http://www.lumileds.com/technology/technology_index.html

Re: White LED\'s other than Blue LED + Yellow Phosphour

interesting stuff. This post was meant to be fun and so others could learn stuff. I always knew the lower wavelengths excited things more. I didn't think about red not charging stuff though, but yes it is true as I've tried it before.

What about using UV to charge white phos? or is white not as effeicent as yellow? Granted, some UV would get past which would have to be tackeled.
Or green led with purple phos? I know there are purple led's with such a phos. Or is green too high of a wavelength to really get the phos going?