Facts About Light Bulb Bases

Screw Bases
Lamps with screw bases have one lead-in wire soldered or welded to the center contact and the other soldered or welded to the upper rim of the base shell. Base shells are typically made of brass or aluminum.

Ceramic Bases
Ceramic bases have internal leads welded to either metal contacts or external lead wires.

Fluorescent Lamp Bases
For Preheat and Rapid Start lamps, four electrical contacts are required, two at each end of the lamp. This is accomplished in the standard line of lamps by use of a miniature bipin for T-5 bulbs and medium bipin for T-12 bulbs. In Circline lamps, the cathodes are connected to a four-pin base located between the junction of the two ends of the lamp. High Output Lamps and Very High Output lamps have recessed double contact (RDC) type bases. Slimline (Instant Start) lamps require only two electrical contacts, one at each lamp end and have single pin bases.

All compact fluorescent lamps that do not have integral ballasts typically have bases with 2 or 4 pins. The 2-pin lamps are designed for preheat operation, and typically have an internal starter. The 4-pin lamps are generally dimmable when used with a dimming ballast and are designed for electronic ballast operation. The 4-pin lamps typically have no need for an internal starter.

Below are some common base types. To view more specific base types click a link from the "Bases" menu at the top left of the page, or click on a light bulb base image below to see an example of a product which uses that base.
Candelabra Base E12
Candelabra/ E12
Intermediate Base E17
Intermediate/ E17
Medium Base E26
Medium/ E26
Mogul Base E39
Mogul/ E39
Bayonet Base
Medium Bipin Base T8
Medium Bi-Pin
Medium Bipin Base T12
Medium Bi-Pin
Miniature Bipin Base T5
Miniature Bi-Pin