They're remarkably heat sensitive, especially cheap ones. Some bulbs would gladly run for 10 years in a room slightly above freezing temperature, but put them in a semi-enclosed fixture in a normal living space, and they're dead in a few months. Fully enclosed fixtures destroy them in no time, unless you buy really exotic bulbs with truly massive aluminum heatsinks, rated for high temp operating environments. I can't even find domestic suppliers for those, and had to order from China.