Abstract: A ballast especially useful in forming symmetrical half cycles of lamp current during dim light level operation, and thus in overcomming a type of lamp flicker. The light level of the lamp is controlled by an intensity selector circuit which controls an auxiliary circuit that, in turn, controls the ballast circuit. The intensity selector circuit comprises an oscillator which produces timing pulses at a frequency controlled by a potentiometer. The oscillator operates a control switch in the auxiliary circuit and the control switch supplies gate current for a power switch. The power switch controls the ballast circuit which turns on the lamp during a portion of each current half cycle; the light level being determined by the length of the conduction portion of that half cycle. The ballast circuit comprises primary, secondary, and heating windings mounted on a common core. The primary winding is connected to ground through a resistor.