A ballast for energizing a lamp at a lighting level selected from a plurality of lamp lighting levels. The ballast includes a buck converter circuit configured to receive a DC voltage signal having a substantially constant magnitude. The buck converter circuit has a duty cycle for generating a lamp voltage output signal from the DC voltage signal. The lamp voltage output signal has a magnitude that is varied by the duty cycle to energize the lamp at the plurality of lamp lighting levels. A controller is configured to receive a dim input signal indicative of the selected lamp lighting level and to provide a control signal to the buck converter circuit as a function of the dim input signal. The control signal indicates a particular duty cycle corresponding to a lamp voltage output signal having a magnitude for energizing the lamp at the selected lamp lighting level.