Edison screw

Edison screw (ES) is a standard socket for light bulbs in the United States. It was developed by Thomas Edison and was licensed in 1909 under the Mazda trademark. Normally, the bulbs have right-hand threaded metal bases (caps) which screw into matching threaded sockets (lamp holders). For bulbs powered by the mains supply, the thread is connected to neutral and the contact on the bottom tip of the base is connected to hot.

In North America and continental Europe, Edison screws displaced other socket types for general lighting. In the early days of electrification, Edison screws were the only standard connector, and appliances other than bulbs were connected to the mains supply via light sockets. Today Edison screw sockets comply with international standards.

Early U.S. lamp manufacturers used different and incompatible bases. The Thomson-Houston Electric Company used a threaded stud at the bottom of the socket, and a flat contact ring. The Sawyer-Mann or Westinghouse base used a spring clip acting on grooves in the bulb base, and a contact stud at the bottom of the lamp. By about 1908, the Edison base was most common in the U.S., with the others falling out of use.

In response to Edison's patent, Reginald Fessenden invented the bi-pin connector for the 1893 World's Fair. Other lamp bases include the bayonet mount and wedge base.

Specifications for all lamp mount types are defined in the following American National Standards Institute (ANSI) and International Electrotechnical Commission (IEC) publications:

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