During the last three weeks, SOME of the lights in my living room, den and bathrooms become dim at times and are normal at other times. (None of the light bulbs in those fixtures have burned out).

This condition does NOT seem to affect lights in other rooms, TVs, computers, appliances and other electrical devices.

Might this problem be with:

the city's power supply
the service panel
the individual circuit breaker(s)
the wires between the circuit breaker and the affected lights
the specific light fixtures
or ???