Why are bulbs burning out quickly in newly installed light fixtures?
I would look for a voltage drop caused by a loose connection in a junction box they tap from or service panel if they all do it, or individually if only certain ones do it. Putting a 100watt lamp in a 40watt socket is a safety(heat)issue (how much heat the fixture is rated to handle), if the fixture cant throw off the heat it would affect the lamps life some, but not that fast.