A ballast for powering a high intensity discharge lamp including an ignitor and a resonant circuit. Ignition pulses produced by the ignitor are added to a boosted low frequency voltage produced by the circuit operating near its resonant frequency during start up of the lamp. The circuit is disabled after a predetermined period of time has elapsed following ignition of the lamp. Application of the signal precedes application of the ignitor pulses to the lamp. Disablement of the circuit can render the ignitor inoperable.