LEDs 50% efficient?! [was Re: alternatives to big oil ...]

From: Robert J. Bradbury (bradbury@www.aeiveos.com)
Date: Thu Feb 03 2000 - 12:13:06 MST

> In a message dated 2/3/00 10:44:50 AM Central Standard Time,
> butler@comp-lib.org writes:
> > Um, a 50% efficiency figure for LEDs sounds a bit on the high side. I'm
> > confident that the efficiency is high. Last I heard, the white light
> > ones are about to push the efficiency of fluorescents/gas-discharge,
> > somewhere around 18%(?), which is pretty darned cool. Ultraefficient red
> > LEDs might be quite a bit higher, like 30-35%.
> >

Mike, now, you know me, I usually add disclaimers when I'm unsure
of something... Though you raise a point, that I did misspeak
in my original message, since I said "LED" when I intended to
say "Laser".

>From "Photonics Spectra" (Optical Industry rag), January 2000, pg 91:
"During the last several years, high-power diode lasers based on
bars have developed rapidly in optical output and in life-time.
In only five years, the typical output form a single commercially
available diode laser has jumped from 20 to 50 W continuous wave (CW),
and typical expected lifetimes increased from 1000 to 10,000 h. This
amounts to a factor of 25 performance increase for commercially available
high-power diode lasers.

The high reliability allows users to combine large groups of diode lasers
to create "stacks." Today diode laser stacks with 20 to 25 individual
diode laser submounts at 40 to 50 W CW each deliver 1 kW or more of
optical output from an area roughtly 10x40 mm. At 50W CW per bar, the
electro-optical efficiency reaches almost 50 percent. This makes the diode
laser the most efficient artificial light source in general."

[These are primarily far-red/near-IR lasers they are talking about.]

Now, I will freely admit that this isn't "white light". However
it is my impression that getting high efficiency lasers is more
difficult than high efficiency LEDs. So where the lasers go,
the LEDs should follow (or maybe they will just use the lasers).
Of course, I don't think I'd be fond of a 3 frequency (RGB),
"white" light, so it would be nice to have some way to broaden
the laser frequencies. But these are just engineering problems.
Since the "blue light" lasers are on a similar trend in terms of
power output and reliability, I think we can say that in the not
too distant future, we "might" have some very efficient light sources.
I say might, because my recent review of the very limited material
on electrodeless fluorescents seems to indicate there *might* be a
manufacturer conspiracy to keep these out of the hands of U.S. consumers.
I'm hoping to get some time over the next week or two to collect
the references for people to peruse. If the same thing were to
happen with white-light laser combinations, we might never see them.

While I don't have the reference handy, I believe the best "lab"
result I've seen is ~65% efficiency.

(Why do I know this stuff??? Because I've got to have some way to
beam all of the energy harvested in space down to the planetary surface
to dismantle it so we can construct the SI. Eugene is such a nit-picker
about not wanting to melt the planet, so I've got to deliver the energy
as efficiently as possible...) Plus, I'm not fond of the spectral
distribution from most fluorescents and I get really tired of changing
the incandescents in my house. Necessity is the mother of research.

On Thu, 3 Feb 2000 EvMick@aol.com wrote:
> I dunno about efficiency numbers but FYI LED's are replacing incadesants
> on trucks.

Naturally, with the way they put panels together now-a-days, it
takes 8 hours to change a light bulb when they burn out.

> The problem is they cost (a LOT) more. But the price is going down.
As the volume increases, that should be the case.


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