Abstract: A circuit is disclosed herein for use in series with a fluorescent lamp and a conventional ballast for supplying operating current to the lamp when the main line source of power has been interrupted. The circuit includes a sensor for detecting the lamp current and utilizes the lamp current for charging a storage battery via a battery charger. An inverter ballast circuit is normally maintained in an "OFF" condition by the sensor and is responsive to the sensor when the power source to the lamp has been interrupted so that the power from the battery is applied to the inverter ballast to turn it to the "ON" condition. Conduction of the inverter ballast circuit provides AC voltage to energize the fluorescent lamp through the conventional ballast.