The Pieces Inside Fluorescent Fixtures

All fluorescent fixtures have the following major components:

• Ballast
• Sockets
• Lamps (a.k.a. light bulbs or tubes) The ballast is like a small transformer inside the fixture.

It has two major jobs:

• First, it provides the spark that sets off the gas within the tube, making that gas fluoresce. This requires higher voltage.
• Then, the transformer reduces the voltage to the (very low) level necessary to sustain lighting.

There are three main types of ballasts or fluorescent circuits: preheat, rapid start, and instant start. (The type is identified on the ballast casing.)
Preheat technology dates back to the original fluorescent fixtures, and it is used today mostly for certain low-wattage fixtures such as compact fluorescent fixtures. This type of circuit uses a starter.
Rapid starts are the most frequently used ballasts today. They maintain a continuous low-wattage circuit to the lamp’s filaments so they start up faster (in less than a second). This style of ballast also comes in a version that allows dimming. An instant-start ballast, as the name implies, ignites the gas in the lamp instantly. It supplies a higher starting voltage than the other types of ballasts, and like the rapidstart variety, it requires no separate starter. The drawback to this voltage boost is that it requires a special lamp. The lamp also will have a shorter life than those used for rapid-start circuits. One way you can distinguish between the lamps is by the number of pins on the ends of the lamp. (These pins insert into the fixture’s sockets or tubeholders.) Rapid-start lamps are bi-pin (they have two pins); most, but not all, instantstart versions have only one.