Discharge lamps are connected to a commerical alternating current power supply through an impedance for blocking high frequency signals and an impedance compensating for the negative resistance of the discharge lamps. The discharge lamps are also connected to the commercial alternating current power supply through a rectifier and oscillator circuit, a voltage signal is generated including the commercial alternating current voltage superposed on a high-frequency, high-voltage signal from the oscillator. This voltage signal is applied to the discharge lamps to energize the same and maintain the lamps in a lighted condition.