Conventional recessed light fixtures tend to be drafty because they create a bridge between a cold attic or roof space and the warm living space below. Cold air drops down (and warm air rises up) through the hole in the ceiling surface---around the edges of the light canister---and through the fixture itself. Although the most energy-wise recessed fixtures today are airtight and rated "IC" (for insulated ceiling; you can cover the fixtures with insulation without creating a fire hazard), standard fixtures are not airtight and cannot be covered with insulation. Therefore, short of replacing the old fixtures with energy-wise models, the only way to stop drafts is to seal around the ceiling holes with caulk.

Instructions
Things You'll Need:

* Silicone caulk
* Caulking gun

1.
Step 1

Turn off the light fixture at the wall switch, and allow the fixture to cool completely.
2.
Step 2

Carefully pull the decorative trim ring on the bottom of the fixture away from the ceiling. Some rings are held to the fixture canister with springs, and you have to reach inside the canister and unhook the springs to remove the rings. Other rings are secured with spring clips that allow you to pull the ring down several inches and let it hang while you work on the fixture.
3.
Step 3

Apply silicone caulk around the outer edge of the fixture canister, sealing any gap between the canister and the ceiling surface. Let the caulk dry overnight, then fit the trim ring back into place.