An apparatus for powering a lamp connected to a ballast circuit. A DC bus provides a DC voltage signal to an inverter. A control circuit selectively energizes the inverter to generate an AC signal for powering the lamp load via the rectifier circuit and an inverter circuit. A detection circuit connected between the lamp and inverter generates a detection signal indicating whether an arc conditionis present in the circuit. The detection circuit also senses the magnitude of the detection signal and generates a command signal to provide to the control circuit to inhibit power from being supplied to the lamp during an arc condition. A switching circuit is coupled between the output of the detection circuit and circuit ground and responsive to an ignition signal from the control circuit to direct the detection signal to ground during an ignition period.