I have never been able to ask the following question and get a simple straight answer and would like to know why there is a controversy, and what the answer really is.
The question: Can a 20 amp 12 AWG circuit for receptacles that are general use receptacles in living areas be used to supply power to a light or two and the switches that control the light or lights? If power is just as easily supplied by a lighting circuit with room on it, then of course one would use that. But if the most convenient supply for the lights is this 20 amp 12 AWG circuit then can it be used?
I have been told yes more times than no. But the no answers have some more detailed take on the issue as it pertains to code.