Lightbulb Base Types

Written by jane ann
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Lightbulb Base Types
There are various types of light bulb bases. (light bulb image by Zoltán Pataki from

Thomas Alva Edison's first light bulb was invented in 1879 and burnt for nearly 15 hours. Today, innovations offer us a wide variety of bulbs in many colours and sizes, including models which last for 60,000 hours. Although there are many types of bulbs, there are only three main light bulb base types; these metal bases connect bulbs with electrical power sources to produce light.

Screw Bases

Light bulbs with screw-in bases are one of the oldest and most common types; they are also known as Edison screw, or ES bulbs, named for their inventor. Distinguish this type from other kinds by examining the bulb for a threaded screw running around the outside of its metal base. To find out if this is the correct type for your requirements, look into your lamp or ceiling lighting fixture to see the threads running around the inside. U.S. bulbs with screw bases are measured in millimetres; these measurements are added to the letter "E" to denote size. Common sizes from small to large include; the E12 candelabra; E17 intermediate; E26, also known as the MES, a standard or medium size; and the E39 mogul. Sizes like E5, a miniature bulb, and E29, a larger medium-sized bulb, are rarer.

Bayonet Bases

Bayonet base light bulbs are less common in the U.S. than Europe. Light bulbs with bayonet bases are fitted by pushing the bulb into the lamp bulb socket, then twisting it to make the electrical contact connect. The most common sizes for bayonet bulbs are 15 and 22mm in diameter. Distinguish this bulb from other kinds by locating the small metal lugs protruding from the sides of the base, which lock into place when twisted in the lamp. Some models have dual-contact bayonet bases; known as DCB bulbs, this means electricity is conducted to the bulb's filament by lugs protruding from the bottom, not the sides, of the base.

Pin Bases

Light bulbs with pin bases come with 1, 2 or 4 pins protruding from the bottom of the bulb to connect it to a light fitting. Pin-base bulbs are measured differently from screw-in base bulbs. The figure in millimetres in the bulb name is a measurement of the distance between the pins, not the diameter of the bulb. Common pin based bulb designations include GU5.3, GU10, G13, MR16 and G23, GX23-2, G24Q-2, GX24Q-3 and GU24. Types of bulbs using pin bases include some models of compact fluorescent light bulb, or CFL, with 2-pin or 4-pin bases and long florescent bulbs with single pins.

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