Patent ID: 8159153

Claim:
A compound light source that generates light of a design intensity at a design temperature in response to a drive current flowing through said light source, said light source comprising: a primary light source; a compensating light source, said primary and compensating light sources converting an electrical current passing therethrough to light, each light source being characterized by an electrical conversion efficiency that decreases with increasing temperature and that also decreases with increasing current; a temperature sensor that measures a temperature of said primary light source; and a current splitting circuit that divides said drive current between said primary and compensating light sources in response to said measured temperature to compensate for said decrease in efficiency of said primary light source with temperature changes above said design temperature, wherein said compound light source emits light having an optical spectrum characterized by a first average wavelength and wherein said primary light source outputs light of an optical spectrum characterized by an second average wavelength, said second average wavelength changing as a function of said temperature and wherein said compensating light source emits light having a third average wavelength chosen to compensate for said change in said second average wavelength as a function of temperature.