Slashdot Mirror
LED's Efficiency Exceeds 100%
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?"
They must have used the wrong cable, causing the light to go faster than C and mess with their readings.
Exceeds 100% ELECTRICAL efficiency is the key here. The conservation of energy is still intact because it supposedly uses heat energy to supplement.
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.
"In this house we obey the laws of thermodynamics!"
My sci-fi novel, Ghost Thief, is now available from Amazon.com.
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.
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
"30 picowatts and measured an output of 69 picowatts of light - an efficiency of 230%. The physical mechanisms worked the same as with any LED: when excited by the applied voltage, electrons and holes have a certain probability of generating photons. 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."
They are not claiming more than 100% efficiency in total terms.
See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
According to TFA, they are actually taking advantage of other sources of energy in addition to the electricity provided by the wall plug. So it's not really the LED getting "greater than 100% efficiency", it's really "producing more light than you would get if you only took advantage of the electricity from the wall plug".
And they're talking in the range of 69 picowatts of light output, using only 30 picowatts of "wall plug" energy input. So it's quite believable.
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.
intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
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
Mimetics Inc. Twitter
Read the article? Heck, I didn't finish the headline. As soon as I realized it didn't mention iPads I went straight to the comments to argue we should instead discuss iPads.
Why don't we have iPad 4 speculation yet?
1. I for one welcome our new iPad 4 overlords and their app that allows you to put hot grits on Natalie Portman and disguise it in a bad car analogy.
2. Ask if it runs Linux, and then cite another failed year of Linux on the desktop.
3. ???
4. Profit.
What were we talking about again?
http://blindscribblings.com - Tasty pop-culture in conceptual fashion.
No it isn't fiddling with numbers. You are missing the heat pump bit.
The device is taking X amount of energy from the electricity supply and X * 1.3 of energy as thermal and converting this to X * 2.3 as light. i.e. it is 230% efficient when comparing light output to electrical input. Equally, it is 100% efficient when comparing light output to electrical and heat energy input combined.
This does take a little bit of thinking to get your head around but I have a more common example in the shed outside. It contains a heat pump which is 350% efficient. It takes 2kW from the electricity supply and outputs 7kW of heat energy to heat my house. The missing 5kW comes from the pipes in the garden as heat energy. The result being that the garden is slowly being cooled. http://en.wikipedia.org/wiki/Heat_pump
wot no sig
In theory.
I'm out of my mind right now, but feel free to leave a message.....
Now, some people might still be bothered by this, because the idea of using ambient heat to do useful work is another one of those "perpetual motion machine" kind of claims. Heat represents a disordered (high-entropy) state, from which you cannot extract useful work. The relevant thought experiment here is the Brownian ratchet: the idea being that you have a ratchet that gets bombarded by random molecular collisions (in water or air, say). The ratchet will turn foreward when a random collision is strong enough, and so over time you can use this turning motion to wind a spring and thus convert random thermal motion into stored energy. The reason this doesn't work in real life is because if random thermal motion is enough to overcome the pawl on the ratchet, then the pawl will be 'hot' enough that it will randomly and spontaneously lift up, turning the wheel backwards. The only way to avoid this is to have the pawl at a lower temperature than the rest of the mechanism: this works, but it's well-known that you can extract useful work from a thermal gradient, so the laws of thermodynamics remain intact.
Coming back to this present result, how does this device use ambient heat to generate useful photons? Sure, it acts as a thermoelectric cooler, establishing a local thermal gradient, but this sounds like 'cheating' in that it's a way to extract energy from the entropy of the surroundings! The very first sentence of the scientific paper addresses this:
Basically, the device is converting high-entropy thermal energy into even higher entropy incoherent electromagnetic radiation (light output). So, the second law of thermodynamics is not violated. Essentially, this device is acting as a way to connect thermal degrees of freedom to E&M degrees of freedom. The system, wanting to increase entropy as much as possible, tries to spread energy through all these degrees of freedom, which means creating some photons at the expense of some of the heat in the material.
It's a neat bit of physics, and will probably have implications for device efficiency and other applications.
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.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
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.
"I have never let my schooling interfere with my education." - Mark Twain
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.
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.
run it through the faster than light cables too
It isn't violating the second law for the same reason it's not violating the first -- the system in question is bigger than the LED itself. It includes the environment from which it is obtaining its energy. Local decreases in entropy are not disallowed.
The enemies of Democracy are
"That's a bright idea, he said coldly."
Also, heat-activated lighting. Also, if you can suck heat from the environment to make light, and then pump the light to solar cells to make electricity, you have a heat-to-electric converter.
Maxwell's demon must be rolling over in his randomly displaced bed right about now.
I've fallen off your lawn, and I can't get up.