Monday, August 27, 2012

230% energy efficient LEDs - Seem to violate first law of thermodynamics

Physicists hell-bent on destroying the universe have come up with a tiny LED that produces 69 Pico watts of light while using just 30 Pico watts of power. That’s an efficiency of above 100%, which should be impossible, but isn’t. And in other breaking news, up is down; black is white and zebras looking the same.
Last week, physicists from MIT published a paper in Physical Review Letters entitled “Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency.” My guess is that most physicists cringe a little bit when they see the phrase “above unity,” because that’s another way of saying either “perpetual motion machine” or “free energy,” both of which are likely to get you branded as either an eccentric (if you’re lucky) or a total crackpot (if you’re not).
Over-unity machines may be impossible, but the LED in this paper definitely put out more than twice as much energy in the form of photons as the researchers fed it in the form of electrons. They found that as they decreased the electrical voltage that went into the LED, the emitted light decreased by a direct proportion, while the input power decreased exponentially. In other words, the less power you put into an LED, the more efficient it gets at producing light, and if you decrease the power enough, you can blow right past the 100% efficiency mark.
So, how does this not totally and completely invalidate the conservation of energy? We have to look at how energy flows through the entire system, not just at the electricity in and light out. When the LED gets more than 100% electrically efficient, it starts to cool itself down, which is another way of saying that it’s stealing energy (in the form of heat) from its environment and converting that heat into those over-unity photons.
This cooling effect has some interesting implications for low-power electronics, but most importantly, we can all rest just a little bit easier knowing that the basic physical rules that frame our perception of the universe have survived for one more day.

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