Good News has confirmed：LED converts heat into light,efficiency >200%!

[akunkeji]

Hello, everyone！

The good news:

LED converts heat into light,efficiency >200%!

A light-emitting diode (LED) that emits more light energy than it consumes in electrical energy has been unveiled by researchers in the US. The device â€" which has a conventional efficiency of greater than 200% â€" behaves as a kind of optical heat pump that converts lattice vibrations into infrared photons, cooling its surroundings in the process. The possibility of such a device was first predicted in 1957, but a practical version had proved impossible to create until now. Potential applications of the phenomenon include energy-efficient lighting and cryogenic refrigeration.
The energy of photons emitted by an LED is dictated by the band gap  of the semiconductor used â€" the energy required to make an electronâ€"hole  pair. When an electron and hole recombine in a radiative process, a  photon carries away the extra energy. The voltage across the LED creates  the electronâ€"hole pairs but its value does not affect the photon  energy, since the semiconductor's band gap is a permanent feature of the  material.
However, it is possible for the individual emitted photons to have  energies that are different to the band gap. The vast majority of  electronâ€"hole recombinations actually result in the production of heat,  which is absorbed by the semiconductor in the form of quantized lattice vibrations called phonons. These vibrations create a heat reservoir that can then boost the energy of photons produced by radiative recombination. In 1957 Jan Tauc at the Institute of Technical Physics in Prague pointed out that, since this provided a mechanism for radiation to remove heat from a semiconductor lattice, there was no barrier in principle to an LED being more than 100% efficient, in which case it would actually cool its surroundings.
Obeys the second law  At first glance this conversion of waste heat to useful photons could appear to violate fundamental laws of thermodynamics, but lead researcher Parthiban Santhanam of the Massachusetts Institute of Technology explains that the process is perfectly consistent with the second law of thermodynamics. "The most counterintuitive aspect of this result is that we don't typically think of light as being a form of heat. Usually we ignore the entropy and think of light as work," he explains. "If the photons didn't have entropy (i.e. if they were a form of work, rather than heat), this would break the second law. Instead, the entropy shows up in the outgoing photons, so the second law is satisfied."
Despite the soundness of the physics, over the past five decades  nobody had managed to demonstrate an LED actually cooling its  surroundings. One way researchers tried to maximize the number of  photons produced was to increase the bias voltage across the LED, but  this also increases the heat produced through non-radiative recombinations.

So, Santhanam and colleagues did the exact opposite and reduced the  bias voltage to just 70 ?V. They also heated the LED to 135 °C to  provide more lattice heat. In this regime, less than 0.1% of the  electrons passing through the LED produced a photon. However, when the  researchers measured the minute power of the infrared radiation produced  by the LED, they measured 70 pW of power being emitted by the LED while  only 30 pW was being consumed, an efficiency of more than 200%. This  happens because as the voltage approaches zero, both light output and  power dissipation also vanish. However, the power dissipated is  proportional to the square of current, whereas light output is  proportional to the current â€" halving the bias voltage therefore doubles  the efficiency.
Important breakthrough  One possible application of the effect is a refrigeration device that removes heat in the form of light. As an expert in this field, Jukka Tulkki of Aalto University in Finland, told physicsworld.com, "I think this is a historically important breakthrough…that could eventually lead to more useful and technologically relevant applications."  However, he cautions that the cooling power of this particular device is extremely low and not great enough for any practical applications.
Santhanam, meanwhile, believes the principle may find applications in  fields other than refrigeration. "My personal opinion is that it's more  likely to be useful as a light source," he says. "Refrigerators are  mostly useful when they are high power. Light sources, however, are used  in all kinds of ways. In particular, light sources used for  spectroscopy and communication don't necessarily need to be very bright.  They just need to be bright enough to be clearly distinguishable from  some background noise."
The research is published in Physical Review Letters.

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[broli]

Wow that's a major breakthrough. Wonder how many years it will take before something useful will come from it. Also makes you wonder about all that cold electricity stuff working with semi conductors.

[Gwandau]

akunkeji,

thanks for the great news.
This is soo cool, 2012 just continues to surprise me.

So many things are surfacing these days and I have a strange feeling
that they are all pieces of the same puzzle, soon changing our situation on earth
far beyond our wildest dreams.

Gwandau

[maw2432]

Check this 50$ LED bulb out.   
http://www.washingtonpost.com/business/economy/government-subsidized-green-light-bulb-carries-costly-price-tag/2012/03/07/gIQAFxOD0R_story.html

[hartiberlin]

Nice confirmation about another  second law violation.

I think they just tried to circumvent to name it this way...

I already tested a few of the new LED bulbs for lighting purposes,
but only very few have good light like a normal light bulb.

You need at least about 800 Lumens to get a good brightness and the cheap chinese
1 to 5 Watt types only have very low Lumens.

A really great new LED light bulb is this one from Philips,
which also recently won the L-Prize.

It is the Philips EnduraLED.

It is the direct replacement for a 60 Watts incandescent bulb and
you can´t see a difference in color rendering.

Check it out here:

http://amzn.to/wO91VS


Regards, Stefan.