Hmm, are you getting this from the paper? It's not obvious to me from the abstract. [0] From the description given, the diode uses current to exchange ambient

Hmm, are you getting this from the paper? It's not obvious to me from the abstract. [0] From the description given, the diode uses current to exchange ambient heat for emitted light. It cools the device, and heats whatever the light falls on, essentially acting as a remote heat pump. We can convert waste heat into a somewhat larger amount of "waste light", effectively increasing black-body radiation, which is great if light is more useful to us than heat. Of course you don't get a free ride, and you can't make something cool without making something else hot (eventually), but conventional air conditioning is bound by the same limitation and is still plenty good enough for our purposes. In principle, what prevents me from covering my roof with these things, radiating my waste heat (less atmospheric absorption) into deep space, and thus cooling my house? Again, this supposing that the device could be scaled up to produce usable amounts of visible light while retaining the local cooling effect at room temperature, none of which have yet been demonstrated. Apparently their technique is to run the diode at as low of a voltage as possible, which presents some obvious problems. [0] http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.108.097403 http://physics.aps.org/synopsis-for/10.1103/PhysRevLett.108.... Actually the abstract states it acts as a "thermodynamic heat engine", which would support what you're saying-- but given that it requires an input of electrical energy, I don't see how that could be right. They also liken it to "thermoelectric coolers". Possibly that was just mistyping or sloppy terminology, or possibly I'm missing something.