A light source having first, second, and third component light sources that are driven by first, second, and third primary drive circuits is disclosed. Each primary drive circuit provides an average current to a corresponding one of the component light sources. A photodetector and processor generate three intensity signals representing the intensity of light produced by each of the component light sources. A servo loop adjusts the drive circuits so as to maintain the intensity signals at corresponding target values. One of the compound light sources includes first and second LEDs that are driven such that the currents through the LEDs are maintained at a fixed ratio by a secondary drive circuit that is connected to the third primary drive circuit. The magnitude of the currents is determined by the third primary drive circuit.