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.