My florescent shop lights have worked for 4 years as well. Even when I dont' get teh spiderwebs cleaned off. Guess my chickens are defective...
The older fluorescents do have a flicker rate that can be harmful to birds, but the newer ones much less so if at all.My only concern about the light bulb is to get it protected from the chickens. My top hen chased one of the young ones off HER spot on the roost (the location of HER SPOT changes almost daily) and the young one jumped/flew high enough to hit the rafters.
Bulbs should definitely be protected from the birds hitting them, maybe hardware cloth covering on tube fixture shades....or barn type fixtures for round bulbs.
My light sits on hardware cloth 'ceiling' in coop...handy.