Patent ID: 8174210

Claim:
Illumination system, comprising: four lamps, each lamp generating light with a respective color point having color coordinates and having a nominal output intensity; four lamp drivers associated with the respective lamps, each lamp driver capable of driving its corresponding lamp with a dim factor (ξ 1 , ξ 2 , ξ 3 , ξ 4 ); a common controller for generating control signals for the lamp drivers such as to control the dim factors (ξ 1 , ξ 2 , ξ 3 , ξ 4 ) of the respective lamps; wherein the controller is responsive to an input signal indicating a target color point (T) having target chromaticity coordinates by calculating target dim factors (ξ 1 T , ξ 2 T , ξ 3 T , ξ 4 T ) and using these values for controlling the drivers; wherein the controller is designed to select one of the lamps to be a basic lamp, to set the dim factor (ξ 4 ) of this basic lamp to be equal to 1, to calculate an optimum solution for the other three dim factors (ξ S , ξ 2 S , ξ 3 S ) as a function of the target chromaticity coordinates, for the maximum allowed value of the luminance for which 0 ≦ξ≦1 applies for each of said dim factors (ξ 1 s,ξ2 s, ξ3 s ); wherein the controller is responsive to an input signal indicating a target brightness (B T ) by calculating said target dim factors (ξ 1 T , ξ 2 T , ξ 3 T , ξ 4 T ) according to (ξ 1 T =B T ·ξ 1 S , ξ 2 T =B T ·ξ 2 S , ξ 3 T =B T ·ξ 3 S , ξ 4 T =B T ·ξ 4 S .