Linear fluorescent lighting is typically used in commercial settings. These are the long fluorescent tube lights in the ceiling. Each tube is held in place with two sockets. The socket type corresponds to the tube type.
Fluorescent tubes can be either T12, T5, or T8 size. The sockets that hold them in place are also T12, T5, and T8 sockets.
Letter and Number
Fluorescent lamps are divided into categories according to their wattage, shape, and diameter. The “T” simply means that the bulb is tubular in shape.
The number indicates the diameter of the lamp in 1/8″ increments. A T8 lamp is 1 inch in diameter and requires a T8 socket. A T5 lamp is 5/8 inch in diameter. A T12 lamp is 1.5 inches in diameter.
Each fluorescent lamp requires two sockets to power the tube and hold it in place. The sockets are either shunted or non-shunted.
The difference between shunted and non-shunted is the flow of the electrical current through the lamp. In a shunted socket, the electrical current flows through a single path. In non-shunted sockets, the current flows through multiple paths.
Typically shunted sockets are only used with instant start ballasts. The non-shunted sockets are used with dimmable ballast, pre-heat, program start ballasts, rapid start ballast, and trigger ballast.
T12, T5, and T8 sockets are available as shunted and non-shunted sockets. Which type to used depends on the size of the lamp and the ballasts.
As technology improved, the T12 lamps were replaced with the more efficient and better quality T8 lamps. T12 lamps use a magnetic ballast while the T8 lamps use an electronic ballast. In addition, the T8 lamps can have either an instant start or rapid start ballast where the T12 did not. The T5 lamps are smaller and brighter than the T8 lamps, but they are also cost significantly more.