Algorithm for color corrected analog dimming in multi-color LED system

A method for controlling a multi-color lighting system for combining light from multiple color sources to produce light of a desired color characteristic, wherein the lighting system comprises three light sources each for producing light of a different one of three colors, each light source comprising one or more light emitters, the method comprising the steps of:

• receiving an input relating to color coordinates of a target point defined in a first color space;
• defining, in the first color space, a first volume having boundaries with endpoints corresponding to color characteristics of the light sources when operated at or near respective maximum intensities, the first volume representing an uncorrected color of a light emitted from the lighting system with a maximum target intensity;
• based on location of the target point in the first volume, identifying a first one of the maximum intensity color characteristics;
• obtaining one first-pass intersection point located in the first volume, at which a line connecting the target point and the endpoint corresponding to a second one of the maximum intensity color characteristics, intersects a boundary line connecting the endpoint corresponding to the first maximum intensity color characteristic and the endpoint corresponding to a third one of the maximum intensity color characteristics;
• obtaining another first-pass intersection point located in the first volume, at which a line connecting the target point and the endpoint corresponding to the third maximum intensity color characteristic, intersects a boundary line connecting the endpoint corresponding to the first maximum intensity color characteristic and the endpoint corresponding to the second maximum intensity color characteristic;
• determining respective amounts of light contributions of the first, second and third maximum intensity color characteristics to system light output for the target point in the first volume, corresponding to the endpoint corresponding to the first maximum intensity color characteristic and the one and the other first-pass intersection points;
• determining first, second and third first-pass driver settings respectively for the first, second and third light sources, based on the determined respective amounts of light contributions of the first, second and third maximum intensity color characteristics;
• when the light is to be dimmed to a proportion of the maximum target intensity, adjusting the first, second and third first-pass driver settings in accordance with the determined respective amounts of light contributions of the first, second and third maximum intensity color characteristics and with the proportion of the maximum target intensity;
• defining, in the first color space, a second volume having boundaries with endpoints corresponding to respective reduced intensity color characteristics of the light sources when operated at the adjusted first, second and third first-pass driver settings;
• based on location of the target point in the second volume, identifying a first one of the reduced intensity color characteristics of the light sources when operated at the adjusted first, second and third first-pass driver settings;
• obtaining one second-pass intersection point located in the second volume, at which a line connecting the target point and the endpoint corresponding to a second one of the reduced intensity color characteristics, intersects a boundary line connecting the endpoint corresponding to the first reduced intensity color characteristic and the endpoint corresponding to a third of the reduced intensity color characteristics;
• obtaining another second-pass intersection point located in the second volume, at which a line connecting the target point and the endpoint corresponding to the third reduced intensity color characteristic, intersects a boundary line connecting the endpoint corresponding to the first reduced intensity color characteristic and the endpoint corresponding to the second reduced intensity color characteristic;
• determining respective amounts of light contributions of the first, second and third reduced intensity color characteristics to system light output for the target point in the second volume, corresponding to the endpoint corresponding to the first reduced intensity color characteristic and the one and the other second-pass intersection points;
• determining first, second and third second-pass driver settings respectively for the light sources based on the determined respective amounts of light contributions of the first, second and third reduced intensity color characteristics;
• and
• applying the determined first, second and third second-pass driver settings, to drive the light sources.

A lighting system, comprising:

• three light sources each for producing light of a different one of three colors, each light source comprising one or more light emitters;
• an input;
• and
• a controller responsive to information received via the input and coupled to control the three light sources to produce a combined light output of the system, wherein the controller is configured to control functions of the lighting system, including functions to:
• receive an input relating to color coordinates of a target point defined in a first color space;
• in a first volume defined in the first color space, having boundaries with endpoints corresponding to color characteristics of the light sources when operated at or near respective maximum intensities, determine first-pass light amounts of respective maximum intensity light contributions from the light sources to achieve light at the target point;
• determine first-pass driver settings for the light sources based on the determined first-pass light amounts;
• when the light is to be dimmed to a proportion of the maximum target intensity, adjust the first-pass driver settings in accordance with the determined first-pass light amounts and the proportion of the maximum target intensity;
• define, in the first color space, a second volume having boundaries with endpoints corresponding to reduced intensity color characteristics of the light sources when operated at the adjusted first-pass driver settings;
• from the second volume, determine second-pass light amounts of respective reduced intensity light contributions from the light sources to achieve light at the target point;
• determine second-pass driver settings for the light sources based on the determined second-pass light amounts;
• and
• apply the second-pass driver settings to drive the light sources to produce a color corrected output light having a color characteristic corresponding to the target point dimmed to the proportion of the maximum target intensity.