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LED's Efficiency Exceeds 100%
New submitter Paul Fernhout writes "Physicists from MIT claim to have demonstrated that an LED can emit more optical power than the electrical power it consumes. Researchers suggest this LED acts like a heat pump somehow (abstract). Is it true that 230% efficient LEDs seem to violate first law of thermodynamics?"
I once observed a low threshold LED (has a much less than 1.4V on-voltage) that was only attached by one lead, with the other lead hanging freely in space. The LED was quite clearly "on". When you put your finger closer to the free hanging lead (but not touch) it got brighter. It was just acting as an antenna in a room with lots of EM radiation around, and the induced current was enough to light it up.
"I have never let my schooling interfere with my education." - Mark Twain
No, and they are using an LED in the far IF spectrum at elevated temperatures. Actually the effect is difficult to distinguish from thermal radiation - a darkening of the LED might also explain it (?). Still, I think the paper is genuine, and under very specific circumstances a combination of thermal and electric energy can power an LED.
The bigger question is: can this be achieved in any real scenario, and not just in minimal amount? That is going to be much tougher.
It's a neat bit of physics, and will probably have implications for device efficiency and other applications.
It's the solution for global warming.
Take a large bank of these over-efficient LEDs. Shine them on a solar panel. Power the LEDs from the solar panel output. Everything in the vicinity of the LEDs gets cold. Make lots of these. Problem solved.
If it seems like a perpetual motion system, it probably is. If you've got a 230% efficient LED, then you can have a 50% efficient solar panel and still come out ahead.
The only problem is what to do with all the excess electricity these things will produce.
I think this could be applied as an interesting method to cool an object by applying a voltage to it... if it consumes both the energy of the voltage and the ambient temperature of the device.
Sounds like the LED is effectively re-directing the thermal radiation then, which is kind of cool. (No pun intended.) Could you daisy-chain this so the light output of one super-powers the next to draw heat away from a source? You'd be siphoning off as much heat energy from the system as the electric energy you're putting in in that case.
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It's already been pointed out that this doesn't violate the first law of thermodynamics, because heat is turned into light. However, it's less obvious how the second law of thermodynamics stays intact. The reason has to do with the temperature difference between the LED and its environment. Notice how the efficiency at room temperature is several orders of magnitude below 1, and only at 135 C do you see an efficiency greater than 1, and only for very, very small output powers. Really, they could have taken any old piece of metal and heated it to 135 C and measured the amount of light generated. It's known as the blackbody effect. The fact that it's an LED is completely irrelevant.
This is just foolish science. It happens all the time. Someone thinks they discovered something new, but really it can be completely understood from fundamental laws.
Yes, to say 230% efficient is really a false statement.
Depends on your perspective. If you are selling these as LED light bulbs that output twice as much energy then they take from the wall plug, then yes, they are 200% efficient. They don't output more energy than what is put into the system, but they do output more energy than you put into the system and since we are all (as a species) self-centered egomaniacs, that is all that matters and the terminology is correct (for the audience).