A light source is disclosed. The light source has a light-emitting chip that includes an LED that generates light in an active region thereof. The LED emits a light signal in a forward direction, and infrared radiation generated in the active region is emitted in a side direction in the form of a first infrared signal. The first light signal is determined by a first drive signal coupled to the LED. The light source also includes an infrared detector positioned to collect a portion of the infrared signal. The infrared detector generates a heat signal indicative of the amount of infrared radiation detected. A controller generates the drive signal so as to maintain the heat signal at a first target value. In light sources having LEDs that emit in different spectral ranges, the infrared detectors can all detect heat in the same spectral range.