Water leaking in from ceiling light fixtures?

If the condensation is wide spread , most likely has to do with heat and cold mixing .Maybe a cold roof with heat penetrating up through the attic will create moisture on the roof side .Same as a cold glass of water in a warm atmosphere .

AC duct leaking cold air in a warm attic will also create condensation .

If it a pin point situation , there should be water marks on the roof side in the attic.

It could be the roof, but then the insulation would be wet as well. It could be a pipe in the ceiling running near the light fixture which is leaking. Leaks are sometimes very hard to find as the water runs to the lowest point and where it originates requires some searching. Get a flashlight, go into the attic and try to find a dampness trail which leads to the origin of the leak. If there isn't any trail, then the pipe leak becomes the next thing to check for.

Keeping the power off to the switch is safe as long as no one turns the switch on i suggest taoing it closed for noe because if you turn off the breaker you will loose all power to that room. Now as far as your leak, pay attention to when it leaks. If its after rain then it is a roof or a gutter problem. If there is another floor between you and the roof possible plumbing problem. Or depending on the contractor that buit your complex maybe you have some of your own plumbing leaking possible vent line for drainage... good luck

High Performance Tactical Flashlight - http://flashlight.uzaev.com/?ZkyT