A method for revealing a light signal error, in particular for railway safety systems, and a device for carrying out the method includes an electronic signal generator, which can be disconnected in a reversible manner in the event of an error, and a control part which is designed for incandescent lamps for controlling and monitoring the signal generator. In order to be able to evaluate the operation of said type of control part with an incandescent lamp interface also when the signal is flashing, it is provided that when the signal generator is activated in the flashing mode, in which no signal voltage is supplied during the flashing intervals, a timer which is connected to a voltage source measures the duration of the pauses between the flashes, and in the event of an error, maintains the disconnection for at least one flashing cycle and signals to the control part.