I have some existing IC-rated cans that I can feel (and see with an IR camera) are leaking cold air from my attic into my living room.

When installing an airtight LED retrofit assembly over it, is it safe to:

  1. Seal the holes inside the can with some sort of insulating foam

  2. Fill the cavity of the can with insulation where the bulb used to occupy, (that is now just an empty space above the LED retrofit assembly)


  • it depends on how hot the cans get. try plugging, run for 1 hour, check the heat with your camera. if ok, run 2 more hours. check again. if ok, they are probably fine. fiberglass won't melt. keep it all under 60C. – dandavis Jan 14 '18 at 21:34
  • Thanks Dan. How do you arrive at the 60C value for "safe" ? – Geremy Jan 16 '18 at 4:04
  • I meant for LED longevity, those things are expensive. For fire safety, you can probably get a lot hotter. MTBF of LEDs shoots down around 70-80C, and there's typically a 10-15C junction-to-surface thermal resistance on retrofit "bulbs" – dandavis Jan 16 '18 at 5:32
  • And what do you mean by "10-15C junction-to-surface thermal resistance on retrofit "bulbs"" ? What is that, and how does it work into the equation here? – Geremy Jan 16 '18 at 18:00
  • junction is the LED's most basic part (a P-N junction). the junction is hotter than the case after operation, by a certain amount. in electronics parts, this whole amount is known as the junction-to-ambient thermal resistance; a fancy term for essentially measuring how hot the engine oil is in relation to the hood. – dandavis Jan 16 '18 at 19:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.