Replacing old ballasts
Fluorescent bulb manufacturers are phasing out the T-12 fluorescent bulbs used in shop lights. The energy-saving T-8 bulbs fit the sockets of the old fixture, but if you don't update the ballast, the new bulbs will burn out in no time. To get the expected life and light output from the new bulbs, you'll have to install a ballast that's right for your fixture and the bulb. Ballasts are rated by the type and number of bulbs the fixture holds. The light output is determined by the “ballast factor.” (This information is on the ballast label.) A high ballast factor means more lumens, but also more energy consumption and shorter bulb life. Ballasts also come in magnetic and electronic versions. We recommend an electronic ballast with a ballast factor of 79 percent or less and an “A” noise rating. That combination will give you adequate light output, low noise (hum), and long bulb life with a minimum of bulb “flicker.”
The downside to updating your ballast is that a ballast costs almost as much as a new fixture. If your fixtures are high-quality ones you want to keep or they're mounted to the ceiling and wired in conduit, you'll save time by installing a new ballast. But if yours are hung by chains and plugged into a receptacle, buying a new fixture may be your best option.
Find electronic ballasts in the lighting department at most home centers. Buy a new ballast based on the type and number of bulbs your fixture holds, as well as on the ballast factor and the sound rating.
Environmental Warning: Old ballasts may contain polychlorinated biphenyls (PCBs), a toxic substance that must be disposed of properly. Bring old ballasts to your local recycling center for disposal.