This is a light switch or light activated switch circuit.The relay on when LDR uncovered and relay off when LDR covered.Adjust VR1 for light sensitive.LED will turn on at the same time with relay.The circuit use LM311 comparator.This circuit need 12Vdc power supply. [...]

Designed for power amps using toroidal transformers, this will limit the inrush current to a sensible value. A PCB is now available for this project. [...]