Some bulbs do just blow, but check just in case that not too much humidity or any water splashes are not getting into the lightfitting. I used to find bulbs almost impossible
to use with high humidity species like water dragons, for this reason. I resorted to ceramic.
This may not be anything to do with it though, maybe a bad batch of bulbs?
Yes I think so too, unless you live in canada where I hear it's freezing still. Chams, even in Yemen
occasionally must have a series of overcast or rainy, or otherwise low temperature days throughout the year. Granted in Yemen it may be few.