A high frequency ballast power supply for a high intensity discharge lamp includes a variable frequency voltage generating circuit for producing a regulated cyclical voltage. After ignition of the lamp, the variable frequency voltage generating circuit operates to vary the frequency of the cyclical voltage over the range of frequencies with a maximum frequency of less than or equal to about 375 kHz. A resonant circuit for regulating the power supplied to the lamp is interposed between the variable frequency voltage generating circuit and the lamp.