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Concept
Edison screw
Summary
Edison screw (ES) is a standard lightbulb socket for electric light bulbs. It was developed by Thomas Edison (1847–1931), patented in 1881, and was licensed in 1909 under General Electric's Mazda trademark. The bulbs have right-hand threaded metal bases (caps) which screw into matching threaded sockets (lamp holders). For bulbs powered by AC current, the thread is generally connected to neutral and the contact on the bottom tip of the base is connected to the "live" phase.
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 light bulbs were connected to AC power via lamp sockets. Today Edison screw sockets comply with international standards.
In the United States, early manufacturers of incandescent lamps used several different and incompatible bases in the 1880s and 1890s. In designing his screw, Edison copied the lid of a kerosene can in his workshop, he even sawed it off to make a prototype in 1880. Another company, the Thomson-Houston Electric Company, used a threaded stud at the bottom of the socket and a flat contact ring. The Sawyer-Man or Westinghouse base used a spring clip acting on grooves in the bulb base and a contact stud at the bottom of the lamp. Most smaller competitors had to produce lamps for all three types, and some used their own designs as well. Other lamp bases include the bayonet mount and wedge base.
All three major designs were patented. Edison himself filed his applications in 1881 and 1890. In response to Edison's patent, Reginald Fessenden invented the bi-pin connector for the 1893 World's Fair.
After some design tweaks Edison settled upon a screw 1 inch in diameter with 7 threads per inch of length, which much later became E26. Screw shells produced as early as 1888 had a lighter taper than the modern ones.
In 1892, Edison General Electric Company merged with Thomson-Houston to found General Electric, which gradually adopted the Edison screw and made it prevalent.
Official source
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