i am an electrician and i mess with alot of ballast and lamps, so my explanation is that something is going out. If everything is securely plugged in and properly wired than only a few things can be wrong: bad bulb, bad ballast, or maybe a socket issue. also these types of lights need a few minutes to reach their brightest light, the ballast and bulb must warm up, if this time starts getting longer than your ballast is going out slowly. try changing just the bulb first, cause they cheaper. them move on to the ballast. the socket also has a tab right in the center that can be mashed down after a while, make sure its dead and stick a flat screw driver inther and pry the tab up a little to ensure contact with the bulb. all i can think of for now but let me know if you need more help. these ballast and bulbs are sold by votage and watts and must match for best results, so be careful to buy the right one.