151007-1017 EDT
The materials in an incandescent bulb can tolerate relatively high temperatures without failure. A small amount of the power input to an incandescent is radiated as visible light, a very large amount as IR radiation (these two components do not affect can temperature very much), and a moderatel amount of input power is output as conducted heat.
The materials in an LED are quite limited in maximum temperature. Probably should be kept under 50-70 C (122-158 F) for good life. The percent of LED input energy that is output in the visible spectrum is high, and is low in the IR range, but high in the conducted range. An insulated and confined space is not good for removal of conducted heat energy.
For a comparable amount of light output you need to put about 6 times more power in to an incndescent compared to an LED. But this does not mean you will get good LED life in a fixture designed for a 60 W incandescent with a 10 W LED installed.
Some temperature rise measurements I made a while ago are described in post 10 of
http://forums.mikeholt.com/showthread.php?t=160447&highlight=led+temperature+rise+in+a+can+fixture .
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