Move the light up the roof and away from any drips to find where the water enters the attic at the dormer.
Roof leak water move around.
Recaulk the corner flashing if any areas have hardened caulk.
Identifying the cause.
The light reflects off the water as it enters the attic near the dormer.
Often wind driven rain comes in from above the roof especially around windows between corner boards and siding and through cracks and knotholes in siding.
The water damage from a roof leak can extend well past the location of the leak.
Dormer walls provide lots of spots where water can dribble down and enter the roof.
Reasons for a roof leak on an external overhang.
Caulk can be old cracked or even missing between the corner boards and between window edges and siding.
Replace any missing or rotted siding above the step flashing on dormers.
Dig out any cracked or dry caulking that isn t properly sealing adjoining surfaces and replace with silicone caulk.
The drip is often.
Even if the roof leak is caused by a windstorm or a tree.
A roof leak is always a cause for concern.
Both are definitely problems but right now you have an even more urgent one because a leak near a light fixture is a serious electrical hazard.