Apply the sealant around the cable and along the edge of the cover where it rests on the ceiling.
Ceiling can lights insulation.
If you have recessed lights installed in the ceiling you need to keep the insulation away from the heat generated by the lights because it is a fire hazard.
Construct a circular dam to place around each can with wire mesh or sheet metal if the lights are not ic rated.
Recessed light in a cathedral ceiling recessed lights often leak warm moist air against cold roof sheathing which eventually causes roof rot.
Now it will be safe to heap insulation onto that spot.
According to the department of energy recessed lights account for 50 of the total thermal losses of a ceiling.
If you re concerned about heat loss through your recessed lights in a cathedral ceiling turn off the light unscrew the bulb and remove the trim to check the label inside.
The lights malfunction is a concern and a safety hazard.
You also lose a lot of heat.
The dam should provide a minimum 3 inch space around the perimeter of the can.