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Fluorescent Tube Diameters Table

Fluorescent Ballasts

T12 Fluorescent Tubes Discontinued

T12 fluorescent tubes are not made anymore because of poor energy efficiency. While these lamps are still in stock in some stores, replacing the ballast with a more efficient T8 electronic ballast could be a better choice.

Fluorescent Ballast Labels

The label on the ballast shows two important labels.

Ballast Wiring Label

Ballast Wiring Diagram

Lamp Compatibility Label

Lamp Compatibility Table

Fluorescent lamps use a ballast which transforms line voltage to a voltage to start up and operate the lamp(s). Newer fluorescent ballasts are usually rated for both 120 volts and 277 volts. Some are rated for only 120 volts, others for only 277 volts (used in commercial environments).

CFLs for the home have a built-in ballast at the base of the bulb. Commercial CFLs use a separate ballast. Ballasts have a wiring diagram to show how they connect to the lampholders.

There are four basic types of fluorescent ballasts:

T8 lamps with a newer electronic ballast use about 20 - 30% less energy than a T12 magnetic ballast. If a T12 magnetic ballast fails, it should be replaced with a T8 electronic ballast. T12 ballasts are available, but T12 lamps are being discontinued. Depending on the light fixture, and how it is mounted, it may be easier and about the same price to replace the fixture instead of the ballast. A new garage fluorescent light fixture could cost less than a replacement ballast.

Fluorescent Tube Sizes

Fluorescent tubes have two common shapes, straight and u-shaped. The most common types are T12, T8, and T5. The T stands for tubular and the number indicates the diameter in 1/8 of an inch. Lamp diameter is determined by ballast type. A fixture with a T12 ballast must use a T12 bulb. A fixture with a T8 ballast must use a T8 bulb, etc.

(4) F32T8


Up to 4 lamps

Fluorescent 32 watts

T8 lamp

Compatible Lamp types for this ballast

(4) F32T8 - Up to four fluorescent lamps, 32 W, T8 lamp.

(4) F25T8 - Up to four fluorescent lamps, 25 W, T8 lamp.

(4) F17T8 - Up to four fluorescent lamps, 17 W, T8 lamp.

Ballast Label T8

Light fixtures with ballasts sometimes have labels that show the required type of lamp and ballast ( F32T8).

Matching a Ballast with a Lamp

There are three requirements when matching a ballast to a lamp. In the example above, lamp type F32T8 has the following three requirements:

1. Fluorescent lamp

2. 32 watts

3. T8.

Fluorescent Ballasts

Ballast Wiring

Parallel Ballast Wiring

Series Ballast Wiring 1 to 3 Lamps

Series Ballast Wiring 4 Lamps

Dimming Ballast Wiring

CFL Ballast Wiring

Emergency Ballasts

Fluorescent Lampholders

Fluorescent Lampholder Wiring

Parallel Ballast Lampholder Wiring

Series Ballast Lampholder Wiring 2 and 4 Lamps

Series Ballast Lampholder Wiring 3 Lamps

Swap Terminals on Non-Shunted Lampholders