Methods, circuits and systems for adjusting chromaticity of solid state lighting

A system to adjust a chromaticity of light emitted by a solid state lighting apparatus including a plurality of light-emitting devices (LEDs) coupled together in a at least one string including a first modulated LED segment, a second modulated LED segment, and at least one additional modulated LED segment, the system comprising:

• a colorimeter configured to measure the chromaticity of the light emitted by the apparatus to provide a measured chromaticity value;
• a control circuit coupled to the colorimeter to receive the measured chromaticity value and configured to couple to the solid state lighting apparatus, wherein the control circuit is configured to modulate the first modulated LED segment and/or the at least one additional modulated LED segment based on respective specified chromaticity values of the plurality of LEDs to provide the light substantially in conformance with a Planckian locus;
• wherein the control circuit is configured to adjust modulation of the first modulated LED segment or the at least one additional modulated LED segment by a shift value based on a difference between the measured chromaticity value and a specified chromaticity value to provide an additional v′ shift in light toward the Planckian locus.

A method of operating a lighting apparatus including a single string of a plurality of light-emitting devices (LEDs) comprising at least one first LED configured to emit first chromaticity light, at least one second LED configured to emit second chromaticity light, and at least one additional LED configured to emit additional chromaticity light, the method comprising:

• measuring a CCT value for light emitted by the single string;
• and
• adjusting current through the at least one additional LED using pulse width modulation responsive to determining that the CCT value for the light emitted by the single string is outside a predetermined specified CCT value in a v′ direction of a chromaticity coordinate space.