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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%

• #### They must have used the wrong cable (Score:5, Funny)

on Thursday March 08, 2012 @02:36PM (#39291047) Homepage

They must have used the wrong cable, causing the light to go faster than C and mess with their readings.

• #### Re:They must have used the wrong cable (Score:5, Funny)

on Thursday March 08, 2012 @02:39PM (#39291095)
They could have reversed the polarity of the diode causing a 100% change in efficiency.
• #### Re:They must have used the wrong cable (Score:5, Funny)

<imipak@yaTOKYOhoo.com minus city> on Thursday March 08, 2012 @02:41PM (#39291141) Homepage Journal

They could have reversed the polarity of the neutron flow, causing the LED to be coupled to the singularity driving the Time Lords' TARDISes.

• #### Re:They must have used the wrong cable (Score:5, Funny)

on Thursday March 08, 2012 @02:54PM (#39291401) Homepage

I thought you had to reverse the tachyon polarity.

Now I'm all confused.

• #### Re:They must have used the wrong cable (Score:5, Funny)

<royallthefourth@gmail.com> on Thursday March 08, 2012 @02:43PM (#39291191)

Ah! Monster cables are good for something after all.

• #### Re:They must have used the wrong cable (Score:5, Funny)

on Thursday March 08, 2012 @02:45PM (#39291233)

They must have used the wrong cable, causing the light to go faster than C and mess with their readings.

It was obviously a Denon AKDL1 Dedicated Link Cable [amazon.com]

• #### Re:They must have used the wrong cable (Score:5, Funny)

on Thursday March 08, 2012 @04:18PM (#39292741)

Nothing can go faster than C. Except Fortran, of course.

• #### LED Cooling (Score:5, Informative)

on Thursday March 08, 2012 @02:39PM (#39291099)
So if I get the article right - LED cooling?

Really puts a whole new perspective on LED clad 'gaming'-machines, which as you know - should have blue LEDs for cooling, and red LEDs for superior overclocking.
• #### There *is* someone who can read! (Score:4, Insightful)

on Thursday March 08, 2012 @02:42PM (#39291177) Journal

11 comments down and finally someone has actually understood enough of the summary to know that they aren't claiming that conservation of energy is dead.

• #### Re:There *is* someone who can read! (Score:5, Funny)

on Thursday March 08, 2012 @02:53PM (#39291381) Homepage Journal

Welcome to slashdot, "enjoy" your stay.

• #### Re: (Score:3)

I want to see how this compares to cold cathodes. :)

• #### Re: (Score:3)

I was thinking about California: all those malls that have lights on 24/7 for security wasting electricity while the AC blasts away to keep the malls cool when they are empty (to avoid having to cycle them hard in the morning). If they can scale this up a factor of ... 1x10^(12+2) ... ugh ... Nevermind.

• #### Re:LED Cooling (Score:5, Funny)

on Thursday March 08, 2012 @05:42PM (#39293851)
Does that mean that in future the lights will stay on when you close the fridge door? That destroys everything I thought I knew!
• #### Re:LED Cooling (Score:5, Informative)

on Thursday March 08, 2012 @06:20PM (#39294407)

Not really functional. Looking at the chart, this works in fairly high temperatures (the curve that exceeds 100% is at 135C) and exceptionally low power input and light output.

Basically they are stating that at extremely low voltage and very high ambient temperature, LED can convert a small portion of heat around itself into luminescence. While interesting, practical applications are going to be minimal due to temperature, power and output luminescence values.

• #### Obligatory Simpsons Quote (Score:5, Funny)

on Thursday March 08, 2012 @02:39PM (#39291117) Homepage

"In this house we obey the laws of thermodynamics!"

• #### Not breaking any laws (Score:5, Informative)

on Thursday March 08, 2012 @02:40PM (#39291125)
From the article: "The researchers didn’t try to increase this probability, as some previous research has focused on, but instead took advantage of small amounts of excess heat to emit more power than consumed. This heat arises from vibrations in the device’s atomic lattice, which occur due to entropy." The other thing to note is that these LEDs are being run at REALLY low power.
• #### The Law (Score:5, Informative)

by Anonymous Coward on Thursday March 08, 2012 @02:41PM (#39291155)

For those wondering about conservation of energy, it's intact. The extra energy comes from heat / vibration in the system.

For those concerned about the second law of thermodynamics, it's not specifically addressed in the article, but the smart money's on entropy increasing in this experiment. The second "law" is really just statistics though (law of large numbers anyone?), and as with most statistics people are still arguing about what it really means. See http://en.wikipedia.org/wiki/Second_law_of_thermodynamics#Controversies and http://en.wikipedia.org/wiki/Fluctuation_theorem

• #### against known laws? (Score:4, Funny)

on Thursday March 08, 2012 @02:43PM (#39291197) Homepage
Definitely GPS timing error.
• #### Kvothe did it first (Score:5, Funny)

on Thursday March 08, 2012 @02:46PM (#39291267) Homepage Journal

It's a good example. The hub of a wagon wheel will be warm to the touch. That heat comes from the motion of the wheel. A sympathist can make the energy go the other way, from heat into motion. I pointed to the lamp. Or from heat into light.

There was an art to choosing your projects in the Fishery. It didn't matter if you made the brightest sympathy lamp or the most efficient heat-funnel in the history of Artificing. Until someone bought it, you wouldn't make a bent penny of commission.

• #### Article not as bold in its claim (Score:3)

on Thursday March 08, 2012 @02:46PM (#39291269) Homepage Journal
I didn't follow through to the abstract, but the article didn't claim to be creating net energy. There could be other causes for more net energy emitted than applied, such as the device being on fire.
• #### A misleading and hyperbolic Slashdot story? (Score:3)

on Thursday March 08, 2012 @02:47PM (#39291287)

Wow I'm totally shocked, what's the world coming to? :) All you have to do is actually read the linked article to see there's no sort of thermodynamic violation of any sort implied, not that most of the people posting here will bother to RTFA.

• #### There is some confusion here (Score:5, Funny)

<circletimessquare&gmail,com> on Thursday March 08, 2012 @02:48PM (#39291297) Homepage Journal

as most people think Light Emitting Diode when they hear LED.

But in this experiment they are referring to a Large Entropic Dilemma.

So the results make perfect sense.

• #### Pooooof (Score:3)

on Thursday March 08, 2012 @02:48PM (#39291305)

Now, all we need is a solar cell with 100% efficiency and we're in business.

• #### Re: (Score:3)

Even if we could only get 50% efficiency- we've got ourselves an expensive device that will produce FREE electricity.

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

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?

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

on Thursday March 08, 2012 @03:33PM (#39292025) Homepage
You mean like Stirling engines? They convert heat into mechanical energy, no? http://en.wikipedia.org/wiki/Stirling_engine [wikipedia.org] 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? ...
• #### Good time to RFTA (Score:5, Informative)

on Thursday March 08, 2012 @02:50PM (#39291325) Homepage

Interesting to see the number of posts saying that this is absolutely not possible - reading through the article, it seems possible and maybe there is enough here to study the phenomena enough to warrant more investigations.

The LED seems to be emitting 69 picowatts (pico = 10^-12) when only 30 picowatts of electricity is being pumped in with a measurable decrease in the temperature of the LED. This implies that the LED is acting as a heat pump, converting heat energy into light. If you've ever seen a Peltier cooler in action (or worked through the operation), it seems like to me this is possible.

Note that the power level this phenomenon is observed at is extremely low - the result is maybe good enough for cooling a few molecules of beer - but I think there is something here that should be investigated to see if any usable applications could come out of it.

myke

• #### Re:Good time to RFTA (Score:4, Insightful)

on Thursday March 08, 2012 @03:10PM (#39291663)

So far... only good enough for cooling a few molecules of beer.

The average man could outrun the first combustion-engine powered vehicles. The first modern computers took up entire rooms, were programmed with punchcards and were much less powerfull than the average 1990's cell phone.

We've got our foot in the door. What if we can improve on this the way we have with computers... and then put thousands of them in an array.

• #### Cold? (Score:4, Interesting)

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?

• #### PN junctions are amazing. (Score:5, Insightful)

on Thursday March 08, 2012 @03:07PM (#39291613) Journal

The semiconductor PN junction is amazing. That's what's fundamentally inside LEDs. When appropriately tuned, PN junctions (a) permit electron flow in only one direction, demonstrating their diode nature, (b) convert current into light, like an LED, (c) convert current into a heat differential, like a Peltier junction cooler, (d) convert light into current, like a photo cell, (e) convert heat differential into current, like a solid-state thermionic energy converter, (f) act like a voltage-tunable capacitor, like a varactor, and more. In fact, to a very coarse first approximation, all PN junctions exhibit each of these characteristics to a greater or lesser degree.

So what's this group done? Shown that an appropriately tuned PN junction (or stack of them, I'd imagine) can be used to simultaneously act as a solid-state thermionic energy converter *and* an LED. Thus, it converts applied electricity to photons, but also converts a heat differential to electricity, which gets converted to photons as well, meaning it's sucking heat out of its immediate evironment. Cool stuff, if you'll pardon the pun.

• #### I saw something like this (Score:5, Interesting)

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.
• #### This is actually possible (Score:5, Informative)

on Thursday March 08, 2012 @03:08PM (#39291639)

This is not as incredible as it sounds. To explain how it works, it is perhaps easiest to start with a simpler device. I could take a brick, connect a battery to it and say "Look! This brick is only consuming one milliwatt of electric power, yet it is emitting one Watt of infrared radiation. That is 100 000 % efficiency!" If I did the same thing at 1 000 degrees Celcius, the brick would even be emitting visible light (wether connected to a battery or not.)

What the people at MIT do is a little more complicated. They don't use the black body radiation directly. Instead they take electrons that would have emitted infrared photons, add some more energy to them, and get visible light. For this to work, they only have to add the difference between the energy of an infrared photon and a visible photon, yet they get the light output of a visible photon. At a temperature of 135 degrees Celcius (that is 275 degrees Farenheit if you happen to live in Belize or the United States) the difference between the black body radiation and visible light was small enough that they managed to get over 100 % efficiency. No laws of thermodynamics were violated.

• #### Incomplete summary (Score:3)

on Thursday March 08, 2012 @04:38PM (#39293007)

I would like to see the entire experiment rather than an incomplete summary. here are a few questions.
2. What was the temperature of the LED as the power was decreased?
3. Was the same effect there if the power was started at 0V and slowly increased?

If it only was present for short periods while the power was decreased the effect might even be a capacitance release of power stored in the LED. In the lower efficiency phase electrons may be stored in the LED and released as the power gets lower.

• #### I always knew... (Score:4, Funny)

on Thursday March 08, 2012 @04:46PM (#39293105) Homepage
• #### Sundiver (Score:3)

on Thursday March 08, 2012 @04:54PM (#39293237)

In the book Sundiver by Robert L. Forward, a research ship traveling inside the Sun gets its drive sabotaged, and they escape by using the cooling laser as a drive, freezing everyone aboard.

Lasers are today used to cool to a few milli Kelvins, and below, very close to absolute zero temperature. The reflected colour of the laser is a little bit less pure, as the thermal vibrations are removed by increasing the entropy of the laser light.

The same principle is going on in this light diode.

• #### Some form of Maxwell's daemon ? (Score:4, Interesting)

<addw@phcomp.co.uk> on Thursday March 08, 2012 @07:55PM (#39295555) Homepage

Is this some form of Maxwell's demon [wikipedia.org], 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.

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