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Edison Screw

When you think of light bulbs, this base probably comes to mind.

Named for Thomas Edison and patented in 1881, the metal, grooved base screws into the light socket to make the electrical connection that powers the light. The metal threads connect to the neutral, while the bottom contact point makes the “hot” connection.

Edisons have an “E” prefix and come in multiple sizes, most commonly the E26, which means the base is 26 millimeters in diameter. This size, interchangeable with the European E27, is the one you see in incandescent, light-emitting diode (LED) and compact fluorescent lamps (CFL) everywhere.

Other sizes are E17, called “intermediate,” and the E12, aka candelabra. There’s also the E39, called the “mogul” base, which is used for things like streetlights and other high-wattage applications.

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Candelabra

Candelabra bases are actually Edison bases, but they’re often listed as a separate category. If you’re looking to replace the lamps in a chandelier or fancy wall sconce, you’re probably looking for bulbs with candelabra bases.

Candelabra bases are 12 millimeters in diameter— smaller than other Edison screw bases— and are thus called E12s.

Candelabra base light bulbs come in several globe styles, like round, pointed, flame-shaped and even tubular. And while you’re replacing the lamps, consider changing to LED. Changing a chandelier bulb isn’t something you want to do often, and LED bulbs last longer and are more efficient.