low voltage photoelectric switch for led spotlight

I need help. I am making an led spotlight to mount on the flagpole and light up the flag at night. I have the lights from a 46 led flashlight. I've attached 2- 3.7v Li rechargeable batteries and a solar cell charger. Everything works great, except I want a photoelectric switch to turn light on and off. Right now, it is on a manual switch mounted to the pole. I cannot find and don't know how to build a 3.7v photocell circuit. I've tried 12v (all I can find except for 120v) and they won't work. I need to know what I need to make a 3.7v circuit/switch, and how to tie it in to the existing system. Can anyone help me? Thanks for any input. I am a novice, so be gentle. BJ

stasterisk8 years ago
Put the photo sensor at the gate of a FET. The transistor acts as a switch, the photosensor acts as a resistor, and modulates the voltage. The voltage at the gate of the FET regulates it turning on and off. You'll probably also want to put the photosensor in a black tube, and point it up at the sky, but also away from the light on the flag.