Patent ID: 8084948

Claim:
A method for changing light intensity in a certain direction of an illumination system capable of emitting light (L) with a variable color, the illumination system comprising at least three dimmable light sources generating respective lights having respective, mutually different colors; the method including the steps of; calculating lamp setting factors (α 1 , α 2 , α 3 ) on the basis of said user input signal for said light sources; calculating a system dim factor (β) on the basis of a user input dim signal (S DIM ); determining a first dim limit value (β 1 ) for which said one light source ( 21 ) reaches a dim limit (I MIN ), wherein β 1 represents said first dim limit value, α 1 represents the lamp setting factor for said one light source, I MIN represents the dim limit of said one light source, and Inom represents a nominal intensity of said one light source; calculating lamp dim factors (δ 1 , δ 2 , δ 3 ) as the product of the system dim factor (β) and said lamp setting factors (α 1 , α 2 , α 3 ), generating control signals such that all dimmable light sources are dimmed by said calculated lamp dim factors (δ 1 , δ 2 , δ 3 ); changing the light intensities of all dimmable light sources in said certain direction while maintaining the color point until one of said light sources reaches said dim limit (I MIN ); maintaining the light intensity of said one light source at its dim limit (I MIN ) and changing the light intensities of the other dimmable light sources in the same certain direction in such a manner that the hue is maintained; wherein the light intensities of the said other dimmable light sources are changed in said certain direction until the absolute or relative saturation (ζ) reaches a predetermined threshold value (ζ T )′; wherein said certain direction is a decrease of intensity and said predetermined threshold saturation value (ζ T ) is approximately equal to 0.5.