I often encounter light fixtures ready to start a fire due to over lamping typical over loading occurs with sigle bulb hall lights rated 60 watts max and some one has put a 100 watt bulb in it also kitchen lights with 4 bulbs marked 60 watts max.
typically the insulation on fixture wire gets hard and brittle and starts to crack including the fixture itself the plastic light socket etc overheats and cracks several small fires i have witnessed have resulted from fixture going to ground and causing an arcfault and breaker not tripping.

I have also seen problem when fixtures are installed and electricain removes protective fiberglass insulation in base of fixture because it is in way of attaching fixture.