If fluorescent light ballasts have gone bad, they might become dim, buzz, change color or go through fast blinking cycles. All parts of the light should be inspected for default before replacement. A multimeter can be used to make certain that it is indeed the ballast itself that has gone bad.
If the light makes a buzzing sound when it is turned on, this also can indicate there is something wrong with the ballast. Bulbs that flicker or don’t light up at all often do so because the ballast is not regulating the electricity properly between the 120-volt current and the bulbs.
The only sure fire way to tell that a ballast is faulty is to connect it to a multimeter, an electronic measuring instrument also known as a Volt-Ohm meter. If the ballast is working properly, the needle moves across the face of the multimeter once it is hooked up. If the fixture is found to have a faulty ballast, it should be replaced with a new unit.
Fluorescent lamp fixtures wear down just like any device. The ballast is the most important part of the light, as it brings in the voltage required to light the bulb. It also controls the current to keep the bulb from shorting out from too much current.