E27

E27 is a standard screw-type lamp base used on many household light bulbs. The “E” denotes the Edison screw, and the number 27 refers to the nominal outer diameter of the screw thread in millimeters, about 27 mm. It is part of the Edison screw family, which also includes smaller bases such as E14 and larger bases such as E40. E27 is the dominant international standard for general lighting in Europe, parts of Asia, Africa, and Oceania, while North America commonly uses E26.

Bulbs with an E27 base include incandescent, halogen, compact fluorescent, and light-emitting diode varieties. They are designed for mains-voltage operation and are used in a wide range of fixtures, including ceiling fixtures, lamps, and wall lights. The base is paired with sockets and fixtures rated for the local mains voltage, commonly 220–240 V in many regions.

Compatibility considerations: E27 and E26 are not interchangeable; the E27 thread is larger, and an E27 bulb will not screw into an E26 socket without an adapter. Conversely, an E26 bulb generally will not fit into an E27 socket. When replacing bulbs, use a bulb with the same base type and appropriate voltage and wattage for the fixture.

Standards and terminology: The E27 base is standardized by international bodies such as the IEC and is sometimes referred to as the large Edison screw. Variants exist, including decorative versions and those designed for dimming or special lamps, but the base remains the same.