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Old 03-14-2019, 12:44 PM
bistander bistander is online now
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Quote:
Originally Posted by padova View Post

Quote:
The researchers, Parthiban Santhanam and coauthors from MIT, have published their study in a recent issue of Physical Review Letters.

As the researchers explain in their study, the key to achieving a power conversion efficiency above 100%, i.e., “unity efficiency,” is to greatly decrease the applied voltage. According to their calculations, as the voltage is halved, the input power is decreased by a factor of 4, while the emitted light power scales linearly with voltage so that it’s also only halved. In other words, an LED’s efficiency increases as its output power decreases. (The inverse of this relationship - that LED efficiency decreases as its output power increases - is one of the biggest hurdles in designing bright, efficient LED lights.)

In their experiments, the researchers reduced the LED’s input power to just 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.
It doesn't seem as the laws of physics were broken this way.

with respect

regards
Thank you Padova,

I was going to mention or point out the same when it was my turn. Effects are a billion times smaller than Aaron claims (pW, picowatts, not mW, milliwatts). Also, it needed elevated temperature, 135C. There is also this, quote from paper.

Quote:
Although the Peltier heat exchange of the injection process is highly nonuniform, on average the device remains very slightly cooled so that in steady state the thermal energy required to pump the emitter flows in from the ambient environment. The net cooling power Pcool is given by the difference between the emitted optical power and the input electrical power and is shown in Fig. 4(a). In terms of the zero-bias resistance Rand the current through the device I, the net cooling power is given by
see paper for equation
Quote:
Note that R is not indicative of a purely irreversible process as in an Ohmic resistance. At low bias, voltage and current are directly proportional and R, measured in ohms, represents their ratio. Equation (2) indicates that net cooling results from competition between a cooling process linear in current and a heating process quadratic in current. Here, low-bias LED operation is analogous to a thermoelectric cooler [24], in which Peltier heat transfer competes with Joule heating to realize heat pumping. In both devices a finite current maximizes cooling power, and at lower currents there is a trade-off between power and efficiency.
Moreover, as sources of irreversibility are removed from the LED, it acts as a reversible Carnot-efficient heat pump [19,25] operating between the lattice and the photon field.
This is a complex, and well done, paper. The part which I quoted above leads me to believe that this phenomena is similar in nature to a heat pump where one deals with COP for the system rather than device (converter) efficiency. In support of my observation, note the author's definition in paragraph one.
Quote:
Here we report the first experimental observa-
tion of electroluminescence in which the ratio of detected optical power to supplied electrical power, known commonly as the wall-plug efficiency (or as the heating coefficient of performance), exceeds unity.
Throughout the paper the authors use wall-plug efficiency.

This research is from 2012. If it had indeed proven a break in conventional foundations of physics, I would have though there would be quite more activity surrounding it. I try to keep abreast of developments in the field and this was the first time I have heard about it. Although interesting, I've spent way more time on it than I would have liked.

Aaron,
You have your own definitions of words and terms which I tend to use in the old fashioned conventional manner. Often it seems like we speak different language. So, to be clear, talking about COP, I use this.
https://en.m.wikipedia.org/wiki/Coef...of_performance

Regards and I hope this addresses your concerns,

bi
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Last edited by bistander; 03-14-2019 at 08:26 PM. Reason: billion was million
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