Recessed lighting is a major source of energy loss. They are effectively holes open to your attic. Each light is a 'mini chimney' that sucks energy out of your home. By code any non-IC light, must have insulation at least 3" away from the fixture. The picture below and the thermal picture on the right, shows what happens.

Fortunately it is possible to remedy these situations without resorting to replacing all the recessed lighting cans. A foil faced foam box is sealed around the light and then buried in a deep blanket of cellulose.