Mx Rey (Fuck ICE) 💜 🏳️⚧️"So, solar panels and LEDs are basically the same--"
"what??"
"They're like speakers and microphones--"
"WHAT!!"
"what??"
"They're like speakers and microphones--"
"WHAT!!"
Spottyfox斑狐狸@rey Wait, what?!
@spottyfox which part
@rey The solar panel - LED part, had no idea
@spottyfox so they're basically the same: semiconductor junctions that deal with photons. if you apply enough light to a LED, it'll produce a voltage. if you apply enough voltage to a solar panel, it'll emit light. neither do a good job of doing the wrong thing, but they do
Zelda 
Atomic FoxEhrm, since forever? It's just that the typical LED junction is very small, so it makes a bad photodetector. In fact any old glass-envelope diode can be used as a photosensor, but they're typically most sensitive in the infrared.
Also, as a rule, light-sensing diodes are reverse-biased, and a lot of LEDs have a very low threshold for breakdown under reverse voltage. I can recall killing a red one when I was a kid by applying 3V from two AAs backward across it, being careless with the little Radio Shack 101 Circuits Lab.
Wilfried KlaebeThere's devices that use one IR LED on the device and another one on the communication adapter, pointed at each other, to do two-way communication.