Patent ID: 7649161

Claim:
A light source comprising: a first mixing chamber comprising a first plurality of LEDs, said first mixing chamber having reflective walls and a primary opening formed at a top area of the first mixing chamber that is covered by a first transparent window plate through which light from said first plurality of LEDs exists exits said first chamber, wherein color shift or intensity change occurs as light from said first plurality of LEDs passes through said transparent window plate; a light pipe structure having a first end optically coupled to said transparent window plate such that light from said first plurality of LEDs that passed through said transparent window plate enters said first end, said light pipe having a second end through which said light exits; and a controller that determines the power applied to said first plurality of LEDs, and a photodetector optically coupled to said second end, said photodetector generating signals indicative of an intensity of light generated by said LEDs, said controller causing said LEDs to be powered such that said signal matches a target value.