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Comment by pflanze | Hacker News Reader

> re-emission in valance holes

Are you talking about single-colour LEDs? Since white LEDs use a "phosphor", just like fluorescent lights, that convert blue or UV light. In fact I thought that the phosphors used by LEDs today are much better than those used by fluorescent lights.

Maybe you're talking about RGB lights, which combine separate reg, green and blue LEDs so that the colour mix can be changed. But even then I thought, unlike lasers, LEDs are not using single frequencies but relatively wide bands (but will still leave gaps between the red, green and blue colours).

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> white LEDs use a "phosphor", just like fluorescent lights

Wow. I didn't know that. So I guess the junction actually emits UV which is converted to visible spectrum? Does that mean they're bad for your eyes if some UV leaks out?

How I thought it worked is that different doping materials are blended in the junction to get a mix of frequencies. Maybe that's impossible.

And yes, sure for RGB clusters the spacing is obvious even to my eyes.

For normal lighting LEDs the diode itself usually emits blue light (440-460 nm). Most of the blue photons are then absorbed by the phosphor or phosphors and reemitted at longer wavelengths (yellow-green to red). This converted light mixed with the remaining blue light gives the white color impression.

So no UV, although there are some concerns about the hazards of blue light. But if you ask me, you get much more blue light onto your retinas by just going outside on a sunny day than you'd ever get from normal LED lighting.

> Does that mean they're bad for your eyes

As far as I can see from distributors, most white LEDs today are using a blue light emitter, so there's no issue with UV. When using white LEDs that use an UV emitter, some glass covering is needed to catch the remainder, from what I've heard from a friend (I've never actually built an LED lamp myself). But it appears that blue LEDs are much more efficient than UV ones and that probably explains why normally white LEDs use blue emitters.

More information here (confirming what I just wrote): https://en.wikipedia.org/wiki/Light-emitting_diode#White

PS. I've been looking into these things to some extent because of all the issues with commercial LED lamps (short life, AC or PWM flickering, colour rendering), and have been thinking of mixing more LEDs together (various single colour ones together with various phosphor-employing ones) so as to mix a more ideal spectrum myself, but I haven't gotten around to actually executing that plan.

> So I guess the junction actually emits UV which is converted to visible spectrum?

The junction usually emits violet, but some blue ones exist too.

It's wasteful to emit UV. Fluorescent lights do it because it's not practical to tune them into visible light, but leds do not share that problem.

I still find it fascinating how confidently people are willing to put out comments with all sorts of strongly worded claims about things they are not knowledgeable on, that turn out to completely wrong.

> I still find it fascinating how confidently people are willing to put out comments with all sorts of strongly worded claims about things they are not knowledgeable on, that turn out to completely wrong.

On the other hand I find it terrifying how many people will spend their lives cowering in quiet ignorance never venturing anything, and never learning anything, all for the fear of looking foolish.

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