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LED's Efficiency Exceeds 100% 502

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?"
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LED's Efficiency Exceeds 100%

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  • Heat Energy... (Score:4, Interesting)

    by Oswald McWeany ( 2428506 ) on Thursday March 08, 2012 @02:49PM (#39291313)

    Surely if this is true the "light" is not the big story.

    If you can take "heat" and convert it into another form of energy that is HUUUUUUUGE NEWS- yes I know, steam engines, etc, but they require a large difference in temperature.

    Imagine if your fridge/freezer- GENERATED power- by taking heat energy and converted it into electricity?

  • Cold? (Score:4, Interesting)

    by wisnoskij ( 1206448 ) on Thursday March 08, 2012 @03:00PM (#39291519) Homepage

    So the lights sucking the heat out of the air and feel physically cold to the touch?
    Does this 230% conversion ration only work in really high heat location or is this in room temperature?
    Would this technology not really work in -40 degree winter environments?

  • by RobinH ( 124750 ) on Thursday March 08, 2012 @03:08PM (#39291637) Homepage
    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.
  • Re:Maybe (Score:5, Interesting)

    by thsths ( 31372 ) on Thursday March 08, 2012 @03:11PM (#39291671)

    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.

  • Re:No (Score:5, Interesting)

    by Obfuscant ( 592200 ) on Thursday March 08, 2012 @03:22PM (#39291835)

    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.

  • by Anonymous Coward on Thursday March 08, 2012 @03:23PM (#39291859)

    While my knowledge and understanding is limited I think that the extra power in the light output comes from heat. So light power out is greater than electrical power in but if you consider thermal power AND electrical power then total efficiency is under 100%. Thus the first law of thermal dynamics is safe.

    Only temporarily. If this device is converting heat into light as a byproduct of converting electricity into light, it's still LESS THAN 100% efficient, it just means it's getting the energy from the environment around it, NOT making it itself, OR it is using its own internal heat, meaning the longer it does this trick, the colder it gets. This provides a fundamental limit, namely 0 Kelvins, assuming it can even operate at all anywhere near that cold. Once it reaches this temp., it should start operating at below 100% efficiency, per the laws of thermodynamics.

    Don't get me wrong, if they have figured out a reverse amplifier transistor, one that uses a small current to bias a PN junction, and then receives energy from the background, they've effectively done what Tesla was trying to do around the time he died, just in a completely different way, making a device that can receive the sun's power indirectly, like an antenna, only it would use the environment itself as the antenna, the very air around it.

    Of course, at the picowatt level, unless they can use 22nm or smaller silicon printing tech to make HUGE numbers of these, I would think they'd be prohibitively expensive. People concerned with what color light they output are not seeing the big picture. This allows us to finally, (and don't mod this funny, I'm not joking) use solar power 24 hours a day, since the sun bakes the earth, and the heat remains even at night, (unless you're some poor SOB who lives in Northern Montana, at high altitude where the temp in the dead of winter, at night, gets real close to absolute zero, they say...)

    I once had an idea like this myself, but never pursued it. My version used conventional refrigeration... It feels good to be vindicated. Guess I should have thrown caution to the wind and built that prototype after all.

    Or, just maybe... they cocked up the experiment, which seems vastly more likely, or they're making it up. Is a bit odd for the usual Slashdot April 1 bullshit. But just to throw this out there, remember everyone, grown men are prone to playing idiotic pranks and getting a cheap thrill from believing others believe them when they make shit up, and feel that at the close of March, each year, that some archaic change to a calendar is adequate excuse to give in to those urges, and act like children. I do not look forward to this particular time of year.

  • Re:Maybe (Score:5, Interesting)

    by boxxertrumps ( 1124859 ) on Thursday March 08, 2012 @03:26PM (#39291903)

    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.

  • Re:No (Score:4, Interesting)

    by arth1 ( 260657 ) on Thursday March 08, 2012 @03:29PM (#39291959) Homepage Journal

    Not only silent, but you can beam the light to an external collector that produces electricity. It's like having a peltier element where the hot side can be in a different building.

  • Re:Heat Energy... (Score:4, Interesting)

    by Ogi_UnixNut ( 916982 ) on Thursday March 08, 2012 @03:33PM (#39292025) Homepage
    You mean like Stirling engines? They convert heat into mechanical energy, no? [] The cool thing about this is that it works at low gradients and is solid state, but having heat engines is not exactly something new. Or have I totally missed what you were on about? ...
  • Re:Maybe (Score:2, Interesting)

    by Anonymous Coward on Thursday March 08, 2012 @03:41PM (#39292173)
    /. still needs a like button for those without mod points.
  • Re:Maybe (Score:5, Interesting)

    by ZeroSumHappiness ( 1710320 ) on Thursday March 08, 2012 @03:43PM (#39292203)

    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.

  • Comment removed (Score:5, Interesting)

    by account_deleted ( 4530225 ) on Thursday March 08, 2012 @03:43PM (#39292209)
    Comment removed based on user account deletion
  • by smaddox ( 928261 ) on Thursday March 08, 2012 @04:35PM (#39292963)

    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.

  • Re:No (Score:5, Interesting)

    by zzsmirkzz ( 974536 ) on Thursday March 08, 2012 @04:52PM (#39293209)

    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).

  • Re:Maybe (Score:4, Interesting)

    by mhajicek ( 1582795 ) on Thursday March 08, 2012 @06:04PM (#39294159)
  • by Alain Williams ( 2972 ) <> on Thursday March 08, 2012 @07:55PM (#39295555) Homepage

    Is this some form of Maxwell's demon [], having the same effect but in a way not so far envisaged ? It seems to me that it takes the heat energy, tops it up with some electrical energy and before that process can reverse it radiates the energy away as light. The radiating away has the effect of the trap door - preventing the reversal.

    This device may not work well if there are many of them that can shine on each other, an incoming photon could knock an electron up into the conducting band leaving a hole behind and generating some heat. Thus to be useful the light that they generate would have to be directed away with little reflection.

  • by Taco Cowboy ( 5327 ) on Thursday March 08, 2012 @08:03PM (#39295627) Journal

    According to TFA, the LED outputs 230% of the input energy by "stealing energy (in the form of heat) from its environment" - in other words, that LED device has a side effect of cooling things down

    Will LED become next generation of cooling appliance?

    BTW, I remember, about 10 years ago, /. had a post about a certain chip that can cool things down using "quantum effect" or something, that a British firm had a patent on it

    I can't find that article right now, but I suspect what happened there and what is happening to the MIT experiment on LED may be similar

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