7 ms·

LED's efficiency exceeds 100%

76 points by brianl 15y ago

joejohnson 15y ago
Can someone explain how this makes sense in terms of conservation of energy?
- vishwam 15y ago
  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.
  - gojomo 15y ago
    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.
- einhverfr 15y ago
  Their "efficiency" is light output vs electrical input. The result is actually that it starts converting heat as well as electricity into light. So you get more energy in light out than you put electricity in. You just put more energy in than electricity.
- jarman 15y ago
  Vaguely like a heat pump - electrical energy stimulates conversion of thermal energy to light. So instead of using electricity to produce light and heat, LED uses electricity and heat to produce light.
jnhnum1 15y ago
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.
- yew 15y ago
  Though most inhabited spaces aren't strictly temperature regulated, so there is still some potential for energy subsidization. There might be some applications in solid-state heat pump technology as well. Actually I would think that the more interesting possibility, given that the field is still maturing.
  - mvzink 15y ago
    Most cooling systems are seem pretty complex/bulky/energy-inefficient to an ignorant sob like me, but if they can make it simple enough to fit into an LED, and the fact that this cooling system relies only on optical output and electricity, it could have a lot of cool applications we haven't thought of.
    - ars 15y ago
      Cooling systems don't have to be complex - lookup peltier cooler. But they are energy inefficient because the laws of thermodynamics requires it. (You can make them more efficient by not cooling as low - trading temperature for volume. In an A/C that would mean instead of a 40 degree drop, do a 20 degree drop, but with twice the air flow. The net result for the living space is the same, but the efficiency is much improved.)
- ars 15y ago
  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.)
  - 15y ago
gojomo 15y ago
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?)
- dullcrisp 15y ago
  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?
  - gojomo 15y ago
    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.)
- ars 15y ago
  No, per the laws of thermodynamics the devices would have to be hotter than the room they illuminate. So you would not be cooling the room - you would be cooling the oven you put the devices into.
mikeknoop 15y ago
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.
- kijin 15y ago
  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.
erikb 15y ago
The article is misleading. Why post it at all?
- mvzink 15y ago
  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.
  - ars 15y ago
    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.
DrStalker 15y ago
Now all we need is a 100% efficient solar panel and we can make a self-powered fridge.
- rplnt 15y ago
  More like an oven as the "over 100% efficiency" is achieved only in high temperatures.
cmcewen 15y ago
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 http://www.cree.com/products/pdf/led%20arrays.pdf
donnawarellp 15y ago
This phenomenon reminds me very much of the method used to create a Bose–Einstein condensate (http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensat...) An exciting posibility would be if a solid state device could be developed to generate BEC, which could lead to super high density optical storage since BEC can trap light.
shubber 15y ago
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.
generators 15y ago
100% electricity power = 90% optical power + 10 % heat loss power 10% heat power = 20% heat movement power. 20% heat movement power = 20% optical power. so, 100% electricity power + 10% atmosphere power = 110% optical power. am i reading this correctly ?

76 points by brianl 15y ago

joejohnson 15y ago

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

vishwam 15y ago
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.
- gojomo 15y ago
  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.
einhverfr 15y ago
Their "efficiency" is light output vs electrical input. The result is actually that it starts converting heat as well as electricity into light. So you get more energy in light out than you put electricity in. You just put more energy in than electricity.
jarman 15y ago
Vaguely like a heat pump - electrical energy stimulates conversion of thermal energy to light. So instead of using electricity to produce light and heat, LED uses electricity and heat to produce light.

jnhnum1 15y ago

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.

yew 15y ago
Though most inhabited spaces aren't strictly temperature regulated, so there is still some potential for energy subsidization. There might be some applications in solid-state heat pump technology as well. Actually I would think that the more interesting possibility, given that the field is still maturing.
- mvzink 15y ago
  Most cooling systems are seem pretty complex/bulky/energy-inefficient to an ignorant sob like me, but if they can make it simple enough to fit into an LED, and the fact that this cooling system relies only on optical output and electricity, it could have a lot of cool applications we haven't thought of.
  - ars 15y ago
    Cooling systems don't have to be complex - lookup peltier cooler. But they are energy inefficient because the laws of thermodynamics requires it. (You can make them more efficient by not cooling as low - trading temperature for volume. In an A/C that would mean instead of a 40 degree drop, do a 20 degree drop, but with twice the air flow. The net result for the living space is the same, but the efficiency is much improved.)
ars 15y ago
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.)
- 15y ago

gojomo 15y ago

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?)

dullcrisp 15y ago
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?
- gojomo 15y ago
  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.)
ars 15y ago
No, per the laws of thermodynamics the devices would have to be hotter than the room they illuminate. So you would not be cooling the room - you would be cooling the oven you put the devices into.

mikeknoop 15y ago

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.

kijin 15y ago
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.

erikb 15y ago

The article is misleading. Why post it at all?

mvzink 15y ago
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.
- ars 15y ago
  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.

DrStalker 15y ago

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

rplnt 15y ago
More like an oven as the "over 100% efficiency" is achieved only in high temperatures.

cmcewen 15y ago

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 http://www.cree.com/products/pdf/led%20arrays.pdf

donnawarellp 15y ago

This phenomenon reminds me very much of the method used to create a Bose–Einstein condensate (http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensate http://en.wikipedia.org/wiki/Bose%E2%80%93Einstein_condensat...) An exciting posibility would be if a solid state device could be developed to generate BEC, which could lead to super high density optical storage since BEC can trap light.

shubber 15y ago

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.

generators 15y ago

100% electricity power = 90% optical power + 10 % heat loss power 10% heat power = 20% heat movement power. 20% heat movement power = 20% optical power. so, 100% electricity power + 10% atmosphere power = 110% optical power. am i reading this correctly ?