Water can show up surprisingly far from where it actually entered but if itís showing up at a ceiling light itís a pretty good bet that itís a roof leak. Examine your roof closely on your hands and knees. Youíll be looking for cracks in the sealant around every penetration and seam. And, of course for a damaged membrane. The leak might be several yards from where it shows up inside. Fortunately most leaks are not very difficult to spot with a close visual inspection. You should be doing inspections of your roof and sidewalls 3 or 4 times a year. Water leaks are serious killers of RVs. I learned my lesson the hard way and it was a very expensive lesson. Good luck.