Here's another in the series of building practices that drive me crazy - recessed can lights. They're so popular that some remodelers carry a shotgun and walk through the house randomly shooting holes in the ceilings to install them.
Those of us in the home performance/energy efficiency field look at these lights as abominations. But you can get models that are rated for insulation contact and are air-tight, so that makes them OK, right?
My buddy (and EVER rater) Sean Lintow has recently reported on the demise of the can light, writing their obituary and even following it up with a 'Part Deuce.' Would that it were true! He makes some good points about lighting in his article, but alas, the can light is still alive and sucking (energy, that is).
My main beef with this cloddish light is that it destroys the integrity of the building envelope. If you've read my Building Science 101 article and other posts on the building envelope, you probably know that I'm a big fan of a having as clean a building envelope as possible, with a continuous air barrier and minimal thermal bridging.
The big problem with can lights, in my opinion, is that they're often installed in the building envelope. Once there, they interrupt the air barrier and increase the infiltration rate in the house. They also interrupt the insulation, and any reader of Flat or Lumpy or my attic stair post knows that even a small flaw there can have seemingly disproportional consequences.
If they're installed in a ceiling with attic above, it's certainly possible to get enough insulation in that part of the building envelope. As you can see in the bottom photo, however, simply putting batt insulation on top of the can lights is not adequate. Hot or cold attic air goes right under the insulation, rendering it useless. The best way to insulate this ceiling would be with a blown product (cellulose or fiberglass).
When recessed can lights are put in vaulted ceilings, however, it's nearly impossible to get enough insulation on top of the can light. In the worst cases, the can lights themselves practically touch the roof deck, creating a thermal bypass that speeds the heat loss in winter or heat gain in summer. Not good!
I'll leave the issue of light quality to the experts in that field, but on the grounds of building science alone, the can light should be canned!