All diodes are also light SENSING is you try hard enough.
You don't have to try hard. Just use it as a photodiode and it magically works. However, if it's inside a plastic case that blocks light, it doesn't.
Due to some law about entropy, efficient processes are necessarily reversible. That's why electric motors - some of the most efficient machines ever invented - are also generators.
All diodes are photodiodes, one has to be esp careful of glass encapsulated diodes. I have had that bite me before.
> However, if it's inside a plastic case that blocks light, it doesn't.
You want an ordinary diode to allow current to flow easily when it senses light? Simple: shine a powerful laser at the plastic-encased diode and it will melt the plastic and liquify the metal, fusing it together and allowing current to flow again. See? You just needed to try harder.
Especially true for LEDs, tried that in the lab once with a flood light, got a few μA out of the LED shortened with the multimeter. Did that with 8th graders, we did other experiments mainly with pv, LEDs and bipolar transistors as well.
The logical question came up more than once: “can we use photovoltaic cells as a light?“. Pretty sure that‘ll work, too, but didn’t try because stuff was expensive then and we didn’t have any broken parts of cells at the time. They probably learned a few things on that day.
Steve Mould of Youtube fame did this:
Why all solar panels are secretly LEDs (and all LEDs are secretly solar panels) - https://www.youtube.com/watch?v=6WGKz2sUa0w
I did try to do that in 8th grade, it worked for a bit but it was quite dim and uneven.