Light socket

Lightbulb sockets, lamp sockets or lampholders provide electrical connections to the lamps and support it in the lighting fixture. The use of sockets allows lamps to be safely and conveniently replaced (re-lamping). There are many different standards for these lampholders, created by de facto and by various standards bodies. A general coding system is a letter or abbreviation followed by a number. Some miniature lamps have wire leads suitable for direct connection to wires; some reflector lamps have screw terminals for wire connections.

The most common type of sockets for mains electricity are Edison screws, used in continental Europe and North America, while bayonet mounts dominate in the Commonwealth countries and in the automotive industry. Fluorescent lamps require a different, typically four-pin design. A broad variety of other socket designs exists, applied for specialized lamp constructions.

Early experimental incandescent lamps had their wire leads connected to screw terminals, but this was inconvenient for commercial use. The Edison organization used simple wooden receptacles with copper strips inside them, when putting lamps on the commercial steamship Columbia (owned and operated by the Oregon Railroad and Navigation Company). These sockets included key switches, but were only useful for upright installations of the bulb. The Edison organization developed a screw-base in 1880, initially also of wood but later made with plaster of Paris. Many competitive designs of lamp sockets flourished in the early era of incandescent lighting, using mutually incompatible electrical contact and mechanical fixing arrangements.

The construction of a lampholder socket defines and limits its intended use. Ceramic insulation can withstand considerably higher operating temperatures than bakelite or other plastics. The electrical components and wires must be designed to carry the intended current plus a safety factor.

The contact surface area, thickness and conductivity of the metal, connection methods and maximum operating temperature must all be considered in the design of a new socket. In addition, mechanical factors such as shape of the socket, fixture mounting and attachment, lamp support, ease of re-lamping and total cost of manufacture must be considered. Sockets designed for ordinary household and industrial use have much more design leeway than those used in precision applications.

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Wikipedia