An adjustable color light source comprising: a light source having different channels for generating illumination of different channel colors corresponding to the different channels; and an electrical power supply selectively energizing the channels using time division multiplexing to generate illumination of a selected time-averaged color wherein the light source includes solid state lighting devices grouped into N channels wherein the solid state lighting devices of each channel are electrically energized together when the channel is selectively energized; and the electrical power supply includes (i) switching circuitry arranged to energize a selected one of the N channels and (ii) a color controller causing the switching circuitry to operate over a time interval T in accordance with a selected time division (f1xT, f2xT, or f3xT) of the time interval T to generate illumination of the selected time-averaged color, wherein the time interval T is shorter than a flicker fusion threshold characterised in that said adjustable color light source further comprises: a broadband photosensor having a detection bandwidth encompassing the channel colors generated by the N channels; and an optical meter receiving a detection signal from the broadband photosensor during each time division and computing a measured optical energy for each time division based at least on the received detection signals; wherein the color controller is configured to adjust the time division (f1xT, f2xT, f3xT) of the time interval T based on the measured optical energies and a setpoint color. a light source having different channels for generating illumination of different channel colors corresponding to the different channels; and an electrical power supply selectively energizing the channels using time division multiplexing to generate illumination of a selected time-averaged color wherein the light source includes solid state lighting devices grouped into N channels wherein the solid state lighting devices of each channel are electrically energized together when the channel is selectively energized; and the electrical power supply includes (i) switching circuitry arranged to energize a selected one of the N channels and (ii) a color controller causing the switching circuitry to operate over a time interval T in accordance with a selected time division (f1xT, f2xT, or f3xT) of the time interval T to generate illumination of the selected time-averaged color, wherein the time interval T is shorter than a flicker fusion threshold characterised in that said adjustable color light source further comprises: a broadband photosensor having a detection bandwidth encompassing the channel colors generated by the N channels; and an optical meter receiving a detection signal from the broadband photosensor during each time division and computing a measured optical energy for each time division based at least on the received detection signals; wherein the color controller is configured to adjust the time division (f1xT, f2xT, f3xT) of the time interval T based on the measured optical energies and a setpoint color. a broadband photosensor having a detection bandwidth encompassing the channel colors generated by the N channels; and an optical meter receiving a detection signal from the broadband photosensor during each time division and computing a measured optical energy for each time division based at least on the received detection signals; wherein the color controller is configured to adjust the time division (f1xT, f2xT, f3xT) of the time interval T based on the measured optical energies and a setpoint color.