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Comment by electrograv | Hacker News Reader

I don't understand. Why can't it cool down more than ambient air? You put in X amount of power, and you get out 2X amount of power as light -- therefore additional energy is being taken in as heat and converted to light. Say you direct that light AWAY from the area through mirrors or something so it doesn't heat anything nearby up. Then, by simple energy thermodynamics, you can show that X amount of energy IS being taken away from this local system and deposited elsewhere as light.

Unless you claim that the LED stops producing the >100% efficiency levels at room temperature, I don't see why you're claiming it can't cool anything down.

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Second law of Thermodynamics. It takes additional energy to move heat up a temperature gradient, and you're not accounting for that. You can't move heat from a cold source to a hot sink without paying for it somewhere.

edit: I don't mind a downvote now and then, but I would really prefer a discussion or explanation to a fire-and-forget downvote.

You pay for it with electricity. That's what a heat pump is, ya?

I'm guessing that your downvoters have a problem with the arrow of time.

> Why can't it cool down more than ambient air? You put in X amount of power, and you get out 2X amount of power as light -- therefore additional energy is being taken in as heat and converted to light.

Light is a more highly ordered form of energy than thermal noise; it can be used to do work. If you could convert thermal noise into light and beam it away, you could use that as the cool side for a heat engine and have a perpetual motion machine.

> If you could convert thermal noise into light and beam it away, you could use that as the cool side for a heat engine and have a perpetual motion machine.

By "beam it away", I assume you mean into space or somewhere else you don't care about heat being. In this case, the cold side of the device isn't the real cold sink, it's just a proxy for the several million cubic lightyears of background-temperature near vacuum which will eventually wind up absorbing the light. Aliens on a distant planet may be able to extract power from the light; bully for them, but I already had to pay extra for shipping, so there's no funny business going on.

What makes you think that violates thermodynamics?

(For what it's worth, "perpetual motion machines" are not outlawed by classical thermodynamics, only those which do additional work. There's nothing in theory which prevents you hooking up a 100% efficient emitter and a 100% efficient receptor up with superconducting wire and letting it run forever, so long as you don't extract any energy from the cycle, for example by observing that it is taking place. There may be something in quantum physics which states that such a system would have to leak information about itself somehow, but I don't know enough to say.)

Why do high-energy lasers need liquid cooling?

Why do LED lamps heat up? If all light sources exhibited thermoelectric cooling, this wouldn't be an invention.

Are you asking something more specific than that?

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