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  1. #1
    Vegan on a bicycle smasha's Avatar
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    Ultra-efficient LED puts out more power than is pumped in

    Ultra-efficient LED puts out more power than is pumped in
    http://www.wired.co.uk/news/archive/...efficient-leds

    The LED produces 69 picowatts of light using 30 picowatts of power, giving it an efficiency of 230 percent. That means it operates above "unity efficiency" -- putting it into a category normally occupied by perpetual motion machines.
    looks like the theoretical luminous coefficient of 683 lm/W may be broken. of course at this point the technology is tiny lights, but the early LEDs and electrical motors were also scientific curiosities with little practical use.
    "When I see an adult on a bicycle, I do not despair for the future of the human race." - H.G. Wells

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    Senior Member Looigi's Avatar
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    Agree. It's just like cold fusion.

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    At first sight this appears to violate the second law of thermodynamics. (To laymen, this is about as bad as violating the law of gravity.) However, the abstract of the paper mentions a "_heated_" LED, so maybe it only works when the LED is kept at a higher temperature than its surroundings. Surely they had to provide some justification to get published in Physical Review Letters, simply claiming to go around the second law of thermodynamics is one of the surest ways to get your paper axed. I can't find full text, this must be the first physics paper in the last 15 years that was not uploaded to arXiv.

  4. #4
    coprolite fietsbob's Avatar
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    My low tech Knee Jerks;

    Watts is not a unit of light output, Its the resistance load, percieved as light
    by things getting hot enough to give off light, in a visible wave length.

  5. #5
    Senior Member 01 CAt Man Do's Avatar
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    Interesting....The tech on this is that the unit draws energy from the environment, likely from ambient heat or from vibration. The kicker is that this is only possible on the micro-scale. As such no real application for bike lighting I'm afraid. However in the future it might be applied to things like cell phones. Whatever the case the amount of energy saved will be minimal when used in practical applications.

  6. #6
    Vegan on a bicycle smasha's Avatar
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    Quote Originally Posted by fietsbob View Post
    Watts is not a unit of light output, Its the resistance load, percieved as light by things getting hot enough to give off light, in a visible wave length.
    no, a Watt is a measure of energy transfer. it can be used to measure...
    * electrical energy applied to an LED, bulb, etc
    * light output from an LED, bulb, etc (more commonly it's used to measure light output of lasers)
    * mechanical energy produced by a bicycle rider or internal combustion engine
    * One kilowatt of power is approximately equal to 1.34 horsepower

    other than "unity" or "lossless" conversion of electrical energy to visible light being 683 lm/W, there's nothing that dictates a correlation between the energy input and visible light output. an incandescent light bulb does this at about 1% efficiency, but that's more efficient that a toaster oven. OTOH, CFLs and LEDs do this with higher efficiency.

    http://en.wikipedia.org/wiki/Watt
    "When I see an adult on a bicycle, I do not despair for the future of the human race." - H.G. Wells

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    You're going to have to break a lot of laws to get more energy out of a system then you put in. So I assume these lights have ZERO heat? I would also assume that they would NEVER fail because no energy would be putting any wear on the LED.
    At best, you could get 1 watt of light for 1 watt of energy and even that is next to impossible. This sounds like people who put electrolysis devices in their cars to get better gas mileage not realizing that they are getting worse mileage.

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    Quote Originally Posted by smasha View Post
    no, a Watt is a measure of energy transfer. it can be used to measure...
    * electrical energy applied to an LED, bulb, etc
    * light output from an LED, bulb, etc (more commonly it's used to measure light output of lasers)
    * mechanical energy produced by a bicycle rider or internal combustion engine
    * One kilowatt of power is approximately equal to 1.34 horsepower

    other than "unity" or "lossless" conversion of electrical energy to visible light being 683 lm/W, there's nothing that dictates a correlation between the energy input and visible light output. an incandescent light bulb does this at about 1% efficiency, but that's more efficient that a toaster oven. OTOH, CFLs and LEDs do this with higher efficiency.

    http://en.wikipedia.org/wiki/Watt
    All lights, all systems are nearly 100% efficient. What incandescent lights lack in light output, they make up for in heat output. What it really is, is how much energy can you get to do the work you want done. Cars are 100% efficient too, just not at moving the car down the road

  9. #9
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    Quote Originally Posted by smasha View Post
    other than "unity" or "lossless" conversion of electrical energy to visible light being 683 lm/W, there's nothing that dictates a correlation between the energy input and visible light output.
    I agree, I'm putting my money on the the conversion being incorrect rather than them finding a perpetual motion machine.

  10. #10
    Senior Member dougmc's Avatar
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    Quote Originally Posted by christo930 View Post
    All lights, all systems are nearly 100% efficient. What incandescent lights lack in light output, they make up for in heat output.
    Of course, when you say "nearly", you mean "exactly"

    (There's also a bit of sound/vibration output (from the 60 Hz input, you can hear it in a really quiet room), a bit of RF output, etc., but add all that up -- 100% efficient.)

    That said, there's an additional complication here. The definition of lumen also includes how sensitive the human eye is to specific wavelengths, and the 683 lumen/W figure is based on the maximum that happens at 555 nm. So any light that was 100% efficient *and* rated at 683 lumens/watt would have to be only one color -- green, 555 nm. Even if the light was 100% efficient (converting all power into visible light) and white, it's lumen rating would be less than 683 lumens/watt.

    So this makes things even worse for this LED. If things were defined differently maybe they could say that their LED was even more efficient because it emits just the right wavelength, but the 683 lumen/watt figure is a maximum, not a minimum or average value.

    As it stands, based on their description, it sounds like much of the energy it's turning into light is coming from a heat engine. That said, that might be quite useful -- perhaps a light powered by combustion, that's much more efficient than candles or wicks?

    Quote Originally Posted by fietsbob View Post
    Watts is not a unit of light output, Its the resistance load, percieved as light
    by things getting hot enough to give off light, in a visible wave length.
    Minor nit -- things do not have to get hot to emit visible light. LEDs do not get particularly hot, fireflies do not get hot, etc. Making things hot is one way of producing visible light, but not the only one. As for the rest, smasha covered it.
    Last edited by dougmc; 02-19-13 at 02:13 PM.

  11. #11
    coprolite fietsbob's Avatar
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    Fireflies use chemistry to emit light.


    Low output red ones in taillights may not get hot,
    but the white ones that light up a fair bit of the highway in the dark
    are using heat sinks to draw off excess heat to make that bright light reliable.

    in the case of my E Delux the aluminum case is directly connected to the
    diode heat sink mount, and so part of the heat dissipation.
    Last edited by fietsbob; 02-19-13 at 11:29 PM.

  12. #12
    Senior Member dougmc's Avatar
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    Quote Originally Posted by fietsbob View Post
    Fireflies use chemistry to emit light.
    But they also produce heat. Just like any other macroscopic light emitting process, it's not 100% efficient. And they're not very bright anyways, so the process doesn't have to emit much heat.

    Low output red ones in taillights may not get hot,
    but the white ones that light up a fair bit of the highway in the dark
    You've misunderstood my point.

    "by things getting hot enough to give off light, in a visible wave length" is indeed one way of generating light. If something gets hot enough (starting at around 1000 degrees F) it will start to emit a significant amount of visible light. This is how incandescent bulbs and the Sun generate light. However, this is only one of several methods by which visible light can be made.

    In the case of an incandescent bulb, the light is emitted because the filament gets hot. But in the case of a LED, it doesn't have to get hot at all to emit light. Yes, it gets warm because the light creation is not 100% efficient, but it's not emitting light because it's getting warm -- it's emitting light due to another process that does not depend on being hot, and the heat is merely a side effect of that process not being 100% efficient.

    Maybe that's not what you meant when you wrote "by things getting hot enough to give off light, in a visible wave length", but that's how it came across, and I pointed out that things don't have to get hot to emit light.

  13. #13
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    My understanding is that these might be used in cooling things.

  14. #14
    Seņior Member ItsJustMe's Avatar
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    Furnaces put out more heat than the electricity that goes into them would warrant. Because they have another energy source besides electricity.

    Same thing here. The LED puts out more light than the electricity that goes into it warrants, because it's getting energy from heat.
    Work: the 8 hours that separates bike rides.

  15. #15
    Reeks of aged cotton duck Hydrated's Avatar
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    Quote Originally Posted by fietsbob View Post
    Fireflies use chemistry to emit light.


    Low output red ones in taillights may not get hot,
    but the white ones that light up a fair bit of the highway in the dark
    are using heat sinks to draw off excess heat to make that bright light reliable.
    Thanks a lot.

    I went to my local pet store to get some low output red fireflies with heatsinks. They just looked at me like I was the one who was nuts!
    It is the mark of an educated mind to be able to entertain a thought without accepting it.-Aristotle

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    Quote Originally Posted by ItsJustMe View Post
    Furnaces put out more heat than the electricity that goes into them would warrant. Because they have another energy source besides electricity.

    Same thing here. The LED puts out more light than the electricity that goes into it warrants, because it's getting energy from heat.
    Ding ding ding! We have a winner.

    One cannot cheat the laws of physics. Energy emitted as light needs to come in as some other form of energy. Energy in will always be greater than energy out.

  17. #17
    Seņior Member ItsJustMe's Avatar
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    Quote Originally Posted by penquissciguy View Post
    Ding ding ding! We have a winner.

    One cannot cheat the laws of physics. Energy emitted as light needs to come in as some other form of energy. Energy in will always be greater than energy out.
    Energy in will always be exactly equal to energy out. Often a lot of the energy out is heat.
    Work: the 8 hours that separates bike rides.

  18. #18
    Vegan on a bicycle smasha's Avatar
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    Quote Originally Posted by ItsJustMe View Post
    Energy in will always be exactly equal to energy out. Often a lot of the energy out is heat.
    or in the case of an electric heater, some of the "wasted energy" is converted into visible light
    "When I see an adult on a bicycle, I do not despair for the future of the human race." - H.G. Wells

  19. #19
    Senior Member dougmc's Avatar
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    Quote Originally Posted by ItsJustMe View Post
    Energy in will always be exactly equal to energy out
    Smart alec answer: what about charging a battery? Doing electrolysis? Pair production? (And yes, I know the answer, you know the answer, so there's no need to give it.)

    I'm not sure why penquissciguy is declaring you to be a winner, it's not like you're the first in this thread to realize that the laws of physics apply even to LEDs.

  20. #20
    Seņior Member ItsJustMe's Avatar
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    Quote Originally Posted by dougmc View Post
    I'm not sure why penquissciguy is declaring you to be a winner, it's not like you're the first in this thread to realize that the laws of physics apply even to LEDs.
    I'm just *A* winner, not the only one
    Work: the 8 hours that separates bike rides.

  21. #21
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    Quote Originally Posted by dougmc View Post
    Of course, when you say "nearly", you mean "exactly"
    Yes, I should have said exactly. All systems are 100% efficient, just not at what you want it to do

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