Photocells are used to automatically turn on and off lights. This device is usually used in places where the air automatically turns on spaces such as courtyards, courtyards and open passages when the air is dark, and turns them off when the air is turned on. Slow down. These sensors act as an open switch when exposed to light, blocking the flow of electricity to the light, and illuminating the power supply when dark like a closed switch. The RSD model is equipped with four wires, 2 of which are used as inputs and two as outputs. The method of wiring and installing them is such that they place it in a place where the sunlight reaches it, so that when the air is turned on, the lamps are turned off in time. This device, like all electrical devices, needs a zero and a phase. .