A ballast to energize a lamp at a selected lighting level is provided. The ballast includes a rectifier, a buck converter, and a controller. The rectifier produces a DC voltage with a substantially constant magnitude. The buck converter generates a lamp voltage output from the DC voltage based on a duty cycle. The output has a magnitude that is varied based on the duty cycle to energize the lamp at a selected lighting level. The controller receives a dim input signal indicating the selected lighting level, and provides an appropriate control signal to the buck converter. The appropriate control signal indicates a particular duty cycle corresponding to magnitude of the output to produce the selected lighting level. In response to receiving the control signal, the buck converter adjusts the duty cycle accordingly, producing the output having the magnitude to energize the lamp at the selected lighting level.