Some time back I found a MOSFET testing circuit that used 2 LEDs on the gate of the MOSFET. When exposed to light the LEDs actually generated enough voltage to turn the MOSFET ON. It was the first and only time I had ever encountered a standard red LED used as a photodiode. Does anyone know this circuit? I cannot find it anywhere and of course, I forgot to make the notes I should have when I found it. I guess I should just grab some parts and start experimenting... What I do remember is that only 1 LED did not work and had to have 2 in series. Thx, Sam.