19. The apparatus of claim 18 , wherein the second period is equal to the first period divided by the number of light channels.
18. A lighting apparatus comprising: a plurality of light channels that operate to produce different spectral distributions of light; a drive circuit coupled to the light channels and programmable to control relative intensities of light output from the light channels; a processor; and a timing circuit coupled to provide to the processor a first signal having a first period and a second signal having a second period that is shorter than the first period, wherein the processor outputs a partial set of parameters for programming of the drive circuit in synchronization with the second signal and provides a complete set of the parameters for programming the drive circuit in synchronization with the first signal.