Circuits, and methods of using same, are disclosed for pulse operating a sodium vapor lamp and, in response to gating pulses applied to a resonant ballast, the lamp ignites to develop a quasi-resonant bidirectional current waveform through the lamp, the shape of which is controlled to suppress the excitation of acoustic resonant nodes in the lamp. The quasi-resonant bidirectional current waveform oscillates at a prescribed frequency and contains a first group of harmonics, the harmonic content of which is outside any acoustic frequency region associated with the lamp, and further contains a second group of harmonics having a harmonic content which coincides with such acoustic frequency region. The current waveform is caused to decay substantially at the time of ignition of the lamp to quickly reduce the magnitude of the second group of harmonics to thereby suppress excitation of the acoustic frequency region and prevent arc instability in the lamp.