Clarification on NEC requirements for Fixtures ( Danger )
I have found even fixture wire in fixtures damaged when larger than specified wattage lamps were used in the past, in several cases the damage may have been a decade old but after several lamp changes the wiring failed. A dimmer can not cause this problem and will reduce the heat generated because the waveform going to the lamp is reduced thus less power less heat. The type of wire needed is fixture wire it is high tempature wire designed to handle the heat but even it can become damaged if a larger wattage lamp is installed than the fixture rating. The next question folks ask is how could 18 gauge wire be legal? It is based on the load of the lamp 60w /120v = .5 amps code allows 18 gauge in signal circuits to be 7 amps. So the wire is large enough but a larger lamp may have cooked the wiring in the past.