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From: Joe Green on 17 Oct 2009 17:39
A friend of mine is into LED lighting. His interest is mostly the replacement market for 60, 75 and 100W tungsten bulbs. I have helped him use RGB LEDs to make white with adjustable color temperature. He says his RGB LEDs do not suffer reduced output or color shift over time. FWIW they get hot and require heat sinks.

Please forgive any technical inaccuracy in this post. Although I have a moderate science background I am mostly repeating what others have said. Those others are electronic and manufacturing engineers. They got their information some from literature and some from others whose knowledge may or may not be accurate.

White LEDs are made from blue LEDs and a phosphor which when excited produces white. These LEDs dim after a few years. My assumption is that the phosphor wears out. When asked I offered a guess that the chemical or physical properties are somehow degraded by exposure to the blue LED.

Wikipedia discusses Phosphor based LEDs but does not address phosphor related reasons for reduced output over time.

Does anyone have any information about this effect? In particular is the effect mostly due to heat or all those high energy blue photons impacting the phosphor?

Thanks,
Joe
From: Androcles on 17 Oct 2009 18:08

"Joe Green" <joe.green(a)hmtown.com> wrote in message
news:17ekd59rokqgternsf0t5np0geim9b0lum(a)4ax.com...
>A friend of mine is into LED lighting. His interest is mostly the
>replacement market for 60, 75 and 100W tungsten bulbs. I have helped him
>use RGB LEDs to make white with adjustable color temperature. He says his
>RGB LEDs do not suffer reduced output or color shift over time. FWIW they
>get hot and require heat sinks.
>
> Please forgive any technical inaccuracy in this post. Although I have a
> moderate science background I am mostly repeating what others have said.
> Those others are electronic and manufacturing engineers. They got their
> information some from literature and some from others whose knowledge may
> or may not be accurate.
>
> White LEDs are made from blue LEDs and a phosphor which when excited
> produces white. These LEDs dim after a few years. My assumption is that
> the phosphor wears out. When asked I offered a guess that the chemical or
> physical properties are somehow degraded by exposure to the blue LED.
>
> Wikipedia discusses Phosphor based LEDs but does not address phosphor
> related reasons for reduced output over time.
>
> Does anyone have any information about this effect? In particular is the
> effect mostly due to heat or all those high energy blue photons impacting
> the phosphor?
>
> Thanks,
> Joe

Although I don't have any data, you should consider the phosphors in
fluorescent tubes which are impacted by even higher energy photons
than mere blue. I have some UV tubes that do just that, and I've not
noticed any deterioration. But then again, I don't use them often so
that doesn't help you much. What is the problem with heat sinks?
Incandescent lamps get hot too, so I don't see what the issue is.



From: zzbunker on 17 Oct 2009 19:13
On Oct 17, 6:08 pm, "Androcles" <Headmas...(a)Hogwarts.physics_p> wrote:
> "Joe Green" <joe.gr...(a)hmtown.com> wrote in message
>
> news:17ekd59rokqgternsf0t5np0geim9b0lum(a)4ax.com...
>
>
>
>
>
> >A friend of mine is into LED lighting.  His interest is mostly the
> >replacement market for 60, 75 and 100W tungsten bulbs.  I have helped him
> >use RGB LEDs to make white with adjustable color temperature.  He says his
> >RGB LEDs do not suffer reduced output or color shift over time.  FWIW they
> >get hot and require heat sinks.
>
> > Please forgive any technical inaccuracy in this post.  Although I have a
> > moderate science background I am mostly repeating what others have said..
> > Those others are electronic and manufacturing engineers.  They got their
> > information some from literature and some from others whose knowledge may
> > or may not be accurate.
>
> > White LEDs are made from blue LEDs and a phosphor which when excited
> > produces white.  These LEDs dim after a few years.  My assumption is that
> > the phosphor wears out.  When asked I offered a guess that the chemical or
> > physical properties are somehow degraded by exposure to the blue LED.
>
> > Wikipedia discusses Phosphor based LEDs but does not address phosphor
> > related reasons for reduced output over time.
>
> > Does anyone have any information about this effect?  In particular is the
> > effect mostly due to heat or all those high energy blue photons impacting
> > the phosphor?
>
> > Thanks,
> > Joe
>
> Although I don't have any data, you should consider the phosphors in
> fluorescent tubes which are impacted by even higher energy photons
> than mere blue. I have some UV tubes that do just that, and I've not
> noticed any deterioration. But then again, I don't use them often so
> that doesn't help you much. What is the problem with heat sinks?
> Incandescent lamps get hot too, so I don't see what the issue is.- Hide quoted text -

Most of the people who use phoshor are trying to generate artistic
light effects,
rather than light or heat anyway
So, that's why the people who actually understand how the phoshor
properties work,
work, on Compact Flourescent Lighting, Flat Screen Software
Debuggers, Electronic Books,
non Vacuum Tube Microcomputers, Atomic Clock Wristwatches, Light
Sticks,
Microwave Cooling, Thermo-Electric Cooling, External non-Rotating
Computer Harddisks,
Multiplexed Fiber Optics, All-In-One Printers, USB, Desktop
Publishing, On-Line Publishing,
Blue Ray, Cyber Batteries, Holographics, and all othee post GE ways
of doing light-heat work.
Rather than Tubes, Heat Sinks or anything else they work on.




>
> - Show quoted text -

From: nuny on 18 Oct 2009 01:18
On Oct 17, 2:39 pm, Joe Green <joe.gr...(a)hmtown.com> wrote:

> White LEDs... dim after a few years.  My assumption is that the phosphor wears out.

Nope. LEDs don't radiate heat as IR the way incandescent filaments
do. Heat causes the dopant atoms to lose their place in the lattice
(migrate), decreasing the flux of emitted exciting radiation. Proof; a
white LED that is dim under its own power glows brightly under
externally-supplied UV.


Mark L. Fergerson
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