Interesting fact of the day. While solar panels do generate some energy from visible light the overwhelming majority is in fact int he infrared part of the spectrum. In fact its peak is well within the infrared but has a black-body like curve.

Since solar panels are essentially just LEDs designed to have maximum surface area this works in both directions. If you apply a voltage to solar panels they will visibly glow in infrared light.

@freemo So, if I blast LED with a strong light, it should generate some/small voltage?

@skyblond Yup you sure can. In fact I've seen people use LED matrices as a poor mans touch screen. You light up the leds and basically measure the current draw. When you block it with your finger it reflects some of the light and changes the current draw slightly. So you can use this to detect where the finger is.

So in this way you can use it as both a light-emitting device AND a light-detecting device at the same time.