An LED is, anyway

Well technically everything is solar in some form or another.

Fossil fuels - dead plants that got their energy from the sun Nuclear(fission) - Uses elements only created from the dying phases of a sun Hydro - Energy that’s created from the sun heating and moving water around Wind - same as above just air instead of water Geothermal - This one is trickier but planets are formed from dead stardust. I guess gravity fits in here somehow. Biomass - see fossil fuels but without as much waiting

The only one I can think of that isn’t solar is nuclear fusion. And this is essentially recreating a star.

Or it's a panel optimized for exploiting infrared light.

It’s not a reverse solar panel. It’s not a solar anything. It requires a difference in heat…

The solar part is because the Sun is responsible for the heat differential.

You're getting downvoted for pointing out that this technology, at optimal efficiency on Earth, generates about 1/100,000 the power of a solar panel. "Not very useful" is an understatement (it's currently fucking useless). Even worse: the title saying "at night" implies a terrestrial usage and misdirects from this technology's only potential useful application in the future once and if it becomes much better – namely on deep-space missions.

This research is interesting. I hope it yields something useful. Your comment is still 100% correct for the foreseeable future.

Edit: I was conflating the optimal efficiency of 1 W/m^2^ and the actual efficiency of 1/100,000 the solar panel. Sorry for introducing that confusion.

Clearly you don't know how much longer sketchy hallways get in the dark. It's at least a 20 fold increase.

Could be good enough for light in dark places

But.. yes

Generally not enough. But maybe with more work they could become better

everywhere

Yeah, that'd be great. Peltiers would be awesome and everywhere if they were dirt cheap.