A light source having a first mixing chamber, a light pipe structure, and a controller is disclosed. The first mixing chamber includes a first plurality of LEDs, the first mixing chamber having a first transparent window through which light from the first plurality of LEDs exits the first mixing chamber. The light pipe structure has a first end optically coupled to the window such that light from the first plurality of LEDs enters the first end and a second end through which the light exits. The controller determines the power that is applied to the first plurality of LEDs and includes a photodetector optically coupled to the second end of the light pipe structure. The photodetector generates signals indicative of an intensity of light generated by the LEDs, the controller causing the LEDs to be powered such that the signal matches a target value.