The standard size for a light fixture socket in the United States is the E26, which measures 26 millimeters, or slightly larger than 1 inch, in diameter at the widest point of the threads. The base has seven threads per inch, uses right-hand threads and meets international standards. Thomas Edison licensed this light fixture socket in 1909 using the Mazda trademark.
Manufacturers also produce other light fixture base sizes for specialty lighting. The E12 or candelabra base is common for use in nightlights, holiday lights and chandeliers. While the intermediate E17 base is less common, some desk lamps and appliances use it. Home fixtures rarely use the mogul E39 base, which is common for street lamps and high-voltage applications.
The Energy Independence and Security Act of 2007 set a schedule to phase out the manufacture and import of many standard incandescent lamps and replace them with more energy-efficient alternatives, such as compact florescent and LED lamps. The replacement lamps use the standard base, though, eliminating any need to replace existing light fixtures in the home. The act does not outlaw the use or purchase of incandescent bulbs, and it allows manufacturers to continue to manufacture them for specialty purposes, such as appliances.