Abstract: A switching circuit, method and control unit (1) for controlling electric power supply for lighting fixtures. The switching circuit has a control unit (1) with a sensor (11) for detecting intensity of light reaching the sensor, and a control circuit (2) for transmitting at least two different switching signals (21-23) at different times in response to the detected light intensity falling below a predetermined twilight value. The circuit further has switching devices (34-36), with a receiver (31-33) for receiving switching signals coming from the output circuit and for selectively generating a switching command for switching on the power supply in response to receiving a switching signal specifically intended for the relevant switching device; and a switching assembly (37-39) connected to the receiver for switching the electric power supply in response to a switching command coming from the receiver.