buildafriend
Well-known member
http://www.lighting.co.uk/news/mit-creates-led-that-cools-its-surrounding-environment/8627537.article
http://prl.aps.org/abstract/PRL/v108/i9/e097403
http://prl.aps.org/abstract/PRL/v108/i9/e097403
improvement upon LED's?
- Thread starter buildafriend
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Thanks for the Physics Review Letters cite. (Tho FWIW, this news is a year old.)
The Physics Synopsis is more understandable:
The energy absorbed by an electron as it traverses a light-emitting diode is equal to its charge times the applied voltage. But if the electron produces light, the emitted photon energy, which is determined by the semiconductor band gap, can be much larger. Usually, however, most electrons create no photon, so the average light power is less than the electrical power consumed. Researchers aiming to increase the power efficiency have generally tried to boost the number of photons per electron. But Parthiban Santhanam and co-workers from the Massachusetts Institute of Technology in Cambridge took a gentler approach, achieving power enhancement even though less than one electron in a thousand produced a photon.
The researchers chose a light-emitting diode with a small band gap, and applied such small voltages that it acted like a normal resistor. With each halving of the voltage, they reduced the electrical power by a factor of 4, even though the number of electrons, and thus the light power emitted, dropped by only a factor of 2. Decreasing the input power to 30 picowatts, the team detected nearly 70 picowatts of emitted light. The extra energy comes from lattice vibrations, so the device should be cooled slightly, as occurs in thermoelectric coolers.
These initial results provide too little light for most applications. However, heating the light emitters increases their output power and efficiency, meaning they are like thermodynamic heat engines, except they come with the fast electrical control of modern semiconductor devices. – Don Monroe
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.108.097403
The Physics Synopsis is more understandable:
The energy absorbed by an electron as it traverses a light-emitting diode is equal to its charge times the applied voltage. But if the electron produces light, the emitted photon energy, which is determined by the semiconductor band gap, can be much larger. Usually, however, most electrons create no photon, so the average light power is less than the electrical power consumed. Researchers aiming to increase the power efficiency have generally tried to boost the number of photons per electron. But Parthiban Santhanam and co-workers from the Massachusetts Institute of Technology in Cambridge took a gentler approach, achieving power enhancement even though less than one electron in a thousand produced a photon.
The researchers chose a light-emitting diode with a small band gap, and applied such small voltages that it acted like a normal resistor. With each halving of the voltage, they reduced the electrical power by a factor of 4, even though the number of electrons, and thus the light power emitted, dropped by only a factor of 2. Decreasing the input power to 30 picowatts, the team detected nearly 70 picowatts of emitted light. The extra energy comes from lattice vibrations, so the device should be cooled slightly, as occurs in thermoelectric coolers.
These initial results provide too little light for most applications. However, heating the light emitters increases their output power and efficiency, meaning they are like thermodynamic heat engines, except they come with the fast electrical control of modern semiconductor devices. – Don Monroe
http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.108.097403
That rules out using them for leg warmers. 
I read about a recent LED improvement where they mimic the scale like pattern in lightning bug's tail light to reduce internal reflections and improve efficiency of LEDs even more.
JR
I read about a recent LED improvement where they mimic the scale like pattern in lightning bug's tail light to reduce internal reflections and improve efficiency of LEDs even more.
JR
gemini86
Well-known member
guys...
think about it...
lightning bug vactrols.
Science, make it happen.
think about it...
lightning bug vactrols.
Science, make it happen.
buildafriend
Well-known member
that might be one of the best digressions on the forum.
I understand most of it but the issue seems to be the low light output due to only one photon per approx every 1000 electrons
I like the idea of stealing from Bioluminescent animals. too bad we can't shove a lightning bug in our circuits. and make it do what we want.
we're almost there.. please excuse the date on this one too.. http://www.youtube.com/watch?v=hFguLwUT5lg
I think what they mean to say is, if you zap a bug it flies away haha.
I understand most of it but the issue seems to be the low light output due to only one photon per approx every 1000 electrons
I like the idea of stealing from Bioluminescent animals. too bad we can't shove a lightning bug in our circuits. and make it do what we want.
we're almost there.. please excuse the date on this one too.. http://www.youtube.com/watch?v=hFguLwUT5lg
I think what they mean to say is, if you zap a bug it flies away haha.
> the issue seems to be the low light output
It's not practical, by a factor of millions+ to 1.
But it seems to be "free energy". The light output is greater than the electrical input.
This is not free or unexpected. Take a Silicon diode at room temperature (any temp other than absolute zero). Short the ends together. A current will flow. Very-very teeny, but the electrons go-round which is current. They will even surmount a teeny external voltage (such as a resistor). This is, in semiconductor lingo, the Saturation Current, meaning the current needed to saturate the small unbalance of crystal charge across a junction.
They may simply have re-discovered Saturation Current. (I acquired a copy of the paper, and intend to read it, but I know it will be heavy work.)
There is a superficially similar effect in thermionic vacuum tubes. Heat the cathode and connect cathode to anode (a grid works too, and the grid is where it can be annoying) through a resistor. There is a voltage across the resistor, thus obviously a current, and real power. (Fractions of a microWatt.) However this is not crystal lattice charge, but the random distribution of electron velocities "sliced" by space-charge (only the faster electrons hit the anode, the others boomerang back to the cathode and we never notice them). Or maybe that's the same thing in a different sort of space? I'm not entirely sure I believe in electrons anyway. Maybe matter and space just seep a continuous electric fluid which only appears to be "lumpy" from far away?
It's not practical, by a factor of millions+ to 1.
But it seems to be "free energy". The light output is greater than the electrical input.
This is not free or unexpected. Take a Silicon diode at room temperature (any temp other than absolute zero). Short the ends together. A current will flow. Very-very teeny, but the electrons go-round which is current. They will even surmount a teeny external voltage (such as a resistor). This is, in semiconductor lingo, the Saturation Current, meaning the current needed to saturate the small unbalance of crystal charge across a junction.
They may simply have re-discovered Saturation Current. (I acquired a copy of the paper, and intend to read it, but I know it will be heavy work.)
There is a superficially similar effect in thermionic vacuum tubes. Heat the cathode and connect cathode to anode (a grid works too, and the grid is where it can be annoying) through a resistor. There is a voltage across the resistor, thus obviously a current, and real power. (Fractions of a microWatt.) However this is not crystal lattice charge, but the random distribution of electron velocities "sliced" by space-charge (only the faster electrons hit the anode, the others boomerang back to the cathode and we never notice them). Or maybe that's the same thing in a different sort of space? I'm not entirely sure I believe in electrons anyway. Maybe matter and space just seep a continuous electric fluid which only appears to be "lumpy" from far away?
