This is a Simple light-operated switch circuit diagram.This light sensitive circuit can operate a relay to switch on lamps or any AC loads when it senses darkness.
It is ideal to use as switch less night lamps. This circuit uses a flip-flop arrangement of Ql and Q2. Normally Ql is conducting heavily. Light on CDS photocell causes Ql bias to decrease, cutting it off, turning on Q2, removing the remaining bias from Q1. Reset is accomplished by depressing S1