Pulse Density Modulation (PDM) is used to control the amount of light from a fluorescent lamp by applying a voltage to the lamp filaments at a low frequency that is approximately at a series resonant frequency of the lamp ballast inductor and the lamp filament capacitor, no voltage and a voltage at a high frequency. The lamp gas ionizes to produce light only when the low frequency voltage is applied. The fluorescent lamp gas does not ionize when the voltage at the high frequency is applied, but the high frequency voltage keeps the lamp filaments warm during low light output conditions. The low frequency, no and high frequency voltages have time periods that occur within a modulation frame time period that repeats continuously. The ratio of the low frequency voltage time period, and the no voltage and/or high frequency voltage time periods determine the light output of the fluorescent lamp.