Automatic fence light is the light where by the light on the fence is automatically switched ON by night and switched OFF by day without the help of anybody or by manual means. The lamp remains ON till morning and then turns OFF during the day time. This eliminates the need of switching the fence light daily and it also helps to lighting the premises when the occupants are out of station. The system makes use of light sensor to operate and sense ambient intensity of light. In an automatic fence light many components are involve in the construction of the circuit. The components includes: transformer, relay, Light Emitting Diode (LED), diode, resistor, capacitor, switch, Vero board and Light Dependent Resistor (LDR). Its working principle is as follows neither the time is day or night, then by night the light switches ON with the help of the Light Dependent Resistor (LDR) and switches OFF by day automatically. Keywords: LDR, LED, AC, Sensor Unit.