A light head for a medical device support system. The light head includes first and second zones of light sources, an optical system, and a control system. The first and second zones of light sources emit respective first and second beams of light that form an illumination pattern having a pattern size at a region of interest. The optical system adjusts a beam spread of the second beam of light to change the pattern size of the illumination pattern from a first pattern size to a second pattern size. The control system varies power to the first and second zones of light sources in response to adjustment of the beam spread of the second beam of light to maintain a substantially constant magnitude of illuminance at the region of interest as the pattern size is changed from the first pattern size to the second pattern size.