John's two are right on. Vibration and a poor connection (heat) are
typical causes. I will add one more. Are the lights you are using for
replacements the same brand and type as the one that is lasting a long time
(they make long life lamps and different shapes etc.).
Also one fixture may have a water leak or be in a position that allows
wind to blow water into the fixture causing problems.
One last thing. Make sure that the socket in the one blowing lamps is
not damaged and that the lamps are making good contact. It the center
contact is bent down or it is corroded or if there are burn marks on it,
that can also cause problems.
Joseph E. Meehan
26 + 6 = 1 It's Irish Math
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