

LED's efficiency exceeds 100% - brianl
http://www.physorg.com/news/2012-03-efficiency.html

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jnhnum1
The linked article and the title are pretty misleading. But if you go and look
at the abstract for the paper, they mention that the extra energy comes from
pumping heat out of the environment.

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ars
Something is missing here. You can not generate energy just from heat you must
have both a heat source and a cold sink. It's en extremely fundamental
thermodynamic law.

Where is the cold source in this experiment? (I'm not saying there isn't one,
just that the article makes no mention of it which is a huge omission.)

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jnhnum1
Energy is certainly not being generated. The energy of the light output will
be equal to the heat absorbed plus the electric energy input.

If you want to think of it in terms of temperatures, I'm a little fuzzy on the
details, but I think in a sense empty space has a temperature associated with
it based on the radiation that is present (similarly to how black body
radiation is a function of temperature).

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ars
I guess if the LED was heated more than the room where you receive the light
it would work.

So you have to put this into an oven for it to work - if you just left it in a
room, and expect it to also put light into that room (i.e. the device and the
room are the same temperature) it would not work.

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mikeknoop
Looking at the figure attached to the article, you can see that the only >
100% efficient trial was with ambient 135 degree-C temperature (two other
trials at 84 degree-C and 25 degree-C were much less efficient). The extra
energy comes from the environment.

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kijin
Still sounds like a promising technology, considering the fact that a lot of
electronics operate in warm environments such as the inside of a computer. If
we could harness a portion of that excess heat and do something useful with
it, that would be pretty cool (no pun intended). Think of a mobile device
whose screen is partially powered by excess heat from the processor, or a
datacenter where some interior lighting is powered by excess heat from the
server racks.

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cmcewen
I'm not sure if this would work the same way, but I know that some high
voltage LEDs are actually just strings of multiple LEDs in series [1]. Though
it clearly wouldn't reach the inflated efficiency in this article, this could
lead to a chip with a large number of very very small LEDs reaching a higher
efficiency than a standard LED. It obviously depends on the manufacturing
process though.

[1] <http://www.cree.com/products/pdf/led%20arrays.pdf>

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DrStalker
Now all we need is a 100% efficient solar panel and we can make a self-powered
fridge.

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rplnt
More like an oven as the "over 100% efficiency" is achieved only in high
temperatures.

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shubber
Wow: 69 whole picowatts of light if the ambient temperature is about 200F. And
fundamentals of the physics mean that neither of those figures is likely to
change.

If the claim were more spectacular, we'd call this snake oil.

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joejohnson
Can someone explain how this makes sense in terms of conservation of energy?

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vishwam
well, they didn't take into account the energy produced by the ambient
temperature (the exact temperature was not mentioned in the article, and the
paper is behind a paywall, but they do say it was rather high)

> [it] instead took advantage of small amounts of excess heat to emit more
> power than consumed. This heat arises from vibrations in the device’s atomic
> lattice, which occur due to entropy.

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gojomo
It'd be nice to know if this meant 'inside an oven' ambient heat, or
Houston/Singapore/Riyadh levels of heat.

 _edit:_ I see from mikeknoop's comment they mean inside-an-oven levels:
135'C/275'F.

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erikb
The article is misleading. Why post it at all?

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mvzink
They turned heat into light using electricity. That may not be what people
were thinking when reading the title/article, but I find this very cool, and I
did not previously know it was possible.

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ars
It's not quite as exciting as you might think.

Heat into electricity is easy with a thermocouple. Electricity into light is
easy with an LED.

And heat into light happens automatically with black body radiation.

It's not nothing though - it's pretty neat to use black body radiation to
boost existing LED light output.

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gojomo
So could you just have a microarray of millions of these to get a practical
amount of light at an insanely-low electricity cost? (And given jnhnum1's
clarification, also be cooling the room slightly?)

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dullcrisp
I may be way off, but I don't think that's how multipliers work. That is, even
if you had a bunch of them, they should still have the same aggregate
efficiency, no?

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gojomo
My thought wasn't about changing the efficiency, but making it useful. The
article mentioned the effect was only evident at very low power levels,
creating very small amounts of light. Light, I believe, does 'add up' so
millions of such devices might provide a useful amount of light while still
having an attractive efficiency. (At least, inside an oven-like environment.)

