I'm slowly replacing the 50 watt halogen MR16 type FNV bulbs we installed during a remodel with LED replacements. This week I changed five sockets in the kitchen, when my batch of replacement LEDs arrived in the morning delivery.

Usually I change lamps when they burn out - but this time the kitchen lamps had all been on for a couple of hours before I changed them, so I noticed how very warm the gypsum board ceiling gets around each 3 inch pot light.

Today while looking for another tool I found my cheap IR thermometer and decided to check the temperature. Around the two remaining halogens, the ceiling showed up to 150 F just next to the lamp! When I was changing the bulbs, internal temperature of some parts read 210 F on our cooking thermometer, when I put the temperature probe on the heat shield for the MR16 bulb; and that was a couple of minutes after unplugging the lamp holder from power.

I checked the temperature of the cover glass and didn't believe what the IR was telling me, so I got out the cooking thermometer and pressed it against the glass - and it went up to 400 F! I thought maybe my thermometer was faulty so I got some fine solder and pressed it to the glass...and it melted. 63/37 electronics solder melts at 361 F. So my thermometer was not lying.

I was horrified at having these heat balls in my kitchen for many years....I imagine the paper on the gypsum board is slowly yellowing away under all that heat.

The LEDs are quite a bit cooler -they are only 7.5 watts each, not 50. The center of the plastic lens gets to about 180 F. Warmer than I expected, but much less dangerous to touch than the glass covers on the halogen-equipped sockets.

I guess this also shows why pot lights are so big, and why there are different types for interior and under-roof lights; if you seal them up to keep out the weather, you also trap all that heat. Even 50 watts over a few hours makes for pretty high temperatures. They need room to dispel the heat, they have only very little air circulation possible in this style of lamp.