I too have had some problems with a dusk to dawn light over my garage. I placed an energy saving florescent bulb in this fixture and it worked great. But the next day I found glass where the bulb apparently busted and the ballast that are built into those types of bulbs was all burned up. Someone told me it was probably because I put a bulb with its wn ballast into a fixture with a ballast. So I installed a HPS bulb& it didn't work then I installed a MH bulb and it didn't work. At this point I figured I burned the ballast in the fixture up but before replacing it I installed a plain flood light and it worked. SO I am guessing my open bottom dusk to dawn fixture has no ballast?