This is the kind of problem that bugs the hell out of me and seems to create more problems than it helps with. There’s a new article out by the website “Lighting”. The article is “MIT creates LED that cools its surrounding environment“.
First, I was skeptical. I mean, lights use energy to generate photons. Since that process isn’t 100% efficient, then there is waste. Since that waste is electricity being passed through a piece of metal, that waste is heat. It’s sort of fundamental.
Then I though, well maybe they use the generated heat to increase the temperature of the LED, somehow creating more light. Something like a halogen lamp does. It gets brighter as it warms up.
Still “cooling its surrounding environment” is a pretty wild claim.
I’ll give this website credit, they do link directly to the peer-reviewed report (which is here). The article sounds pretty impressive “Thermoelectrically Pumped Light-Emitting Diodes Operating above Unity Efficiency”. The abstract is really cool.
A heated semiconductor light-emitting diode at low forward bias voltage V<kBT/q is shown to use electrical work to pump heat from the lattice to the photon field. Here the rates of both radiative and nonradiative recombination have contributions at linear order in V. As a result the device’s wall-plug (i.e., power conversion) efficiency is inversely proportional to its output power and diverges as V approaches zero. Experiments directly confirm for the first time that this behavior continues beyond the conventional limit of unity electrical-to-optical power conversion efficiency.
So, I was kind of right, the internal heat of the LED causes an increase in the emission of photons. Basically, the less voltage applied, the more light is generated. This is amazing. We’re talking a revolution in lighting. The popular article (and abstract) don’t set any limits. Man, I can’t wait until next year, when it’s really hot, I’ll just turn on the lights and help cool the house. Automotive lights could actually cause a cooling effect for the environment. This is so awesome.
Now, let’s look at a synopsis provided by the journal.
Decreasing the input power to 30 picowatts, the team detected nearly 70 picowatts of emitted light.
Wow, the light output was more than double… wait… what…
70 PICOwatts!??!!?
A picowatt is equal to one trillionth (10−12) of a watt. An LED producing 70 picowatts worth of light is 1/1,000,000,000,000 the light of a 70 Watt light bulb.
Now, look at what the synopsis author actually says.
The extra energy comes from lattice vibrations, so the device should be cooled slightly, as occurs in thermoelectric coolers. (my emphasis)
The experiment didn’t show a cooling effect, though it probably wasn’t looking for one. And the cooling effect from trillionths of watts must be pretty miniscule.
This isn’t ready for production technology here, unlike what is implied in the popular article. And the popular article states unequivocally that the light ‘cools its surrounding environment’. But they don’t actually know that. It should happen, but it hasn’t been tested yet.
Still, this is a cool system, no doubt. The big question is, can it be scaled up to production size. A lot of things that work very well in the lab and under tightly controlled conditions don’t work in the home.
My problem here is that the popular article misleads the reader. By not stating that the cooling effect is presumed, but not tested and that this only works (so far) at miniscule voltages (producing miniscule light), the reader is left wondering when they’ll be able to buy a light that cools the room. The answer is, most likely, never.
I know most reporters aren’t scientists and that they don’t always have control of their articles, but this sloppy science reporting, IMO, harms science. It’s making promises that science may not be able to keep.
This certainly isn’t an isolated occurrence. The recent flap over mammal evolution has led to a lot of misunderstanding and misrepresentation in the popular media, for just one example.
I think that we should expect science reporting to be accurate and not hype.
