Understanding Light Bulb Base Types: Screw Bases

Have you ever found yourself shopping for light bulbs but with no clue as to what will fit your fixture? It’s easy enough to look at the bulb that you need to replace and shop for a bulb with a similar looking base, but how will you know for sure if the bases are identical? For example, there are many different bulbs that are the same shape and even have similar looking bases, but those bases might be different sizes. You need to know the technical name for bulb bases. First you have to determine if it’s a screw, bayonet, wedge, or bi-pin base. This post covers screw bases.

Screw-base bulbs, often called Edison bulbs, are named after their inventor—Thomas Edison. In North America and Europe, these light bulb base types are the most common and widely used. Each base type has a descriptive term, such as medium, intermediate, candelabra, etc., and they’re defined by the letter E (Edison) followed by numbers. The numbers refer to base width in millimeters. There are several types of screw bases.

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E26/E27 Medium – Edison 26-mm or 27-mm Diameter

E26 bulbs are primarily used in North America while E27 bulbs are most popular in Europe. Bulbs with these base types can be used interchangeably as there is only a 1-millimeter difference in base size. Bulbs with these bases are the most popular of all screw base bulbs. They are commonly used for general lighting in standard light fixtures, such as ceiling lights, lamps, can lights, outdoor spotlight and flood light fixtures, and vanity lights. Bulbs with these base types are available in many different styles.

Common bulbs with E26/E27 bases:

A-shaped bulbs: A19, A15, A21

Globe-shaped bulbs: G30, G25, G16.5

PAR (parabolic aluminized reflector) spotlight and flood light bulbs: PAR16, PAR20, PAR30, PAR38

BR (bulged reflector) spotlight and floodlight bulbs: BR20, BR30, BR40

A19 bulb

E12 Candelabra – Edison 12-mm Diameter

Bulbs with E12 bases are commonly used for decorative applications, such as chandeliers, wall sconces, Christmas lights, restaurant pendant lights, ornamental lights, residential or commercial string lights, and night lights. Many bulbs with these bases are designed to mimic the look of a candle flame.

Common bulbs with E12 bases:

Small tube-shaped bulbs: T8, T6, T22

Candle-flame-shaped bulbs: C7, C9, CA10, B10

Small globe-shaped bulbs: G14, G16, G50

CA10 bulb

E14 European – Edison 14-mm Diameter

Bulbs with E14 bases are popular in Europe and China for chandeliers, wall sconces, lamps, Christmas lights, restaurant pendant lights, ornamental lights, residential or commercial string lights, sign and marquee lights, and night lights.

Common bulbs with E14 bases:

A-shaped bulbs: A15

Small tube-shaped bulbs: T8, T6, T22

Candle-flame-shaped bulbs: C7, C9, CA10, B10

Small globe-shaped bulbs: G14, G16, G50

Marquee and sign bulbs: S11

S11 Bulb

E17 Intermediate – Edison 17-mm Diameter

Like candelabra bulbs with E12 bases, bulbs with E17 bases are used for decorative applications, such as chandeliers, wall sconces, Christmas lights, restaurant pendant lights, ornamental lights, and sign or marquee lights. Bulbs with these bases are commonly used for appliance lights, such as microwave lights, refrigerator lights, and range hood lights. They’re also found in ceiling fan light fixtures.

Common bulbs with E17 bases:

A-shaped bulbs: A15

Small tube-shaped bulbs: T8, T6, T22

Candle-flame-shaped bulbs: C7, C9, CA10, B10

Small globe-shaped bulbs: G14, G16, G50

Marquee and sign bulbs: S11

T22 Bulb

E39/E40 Mogul – Edison 39-mm or 40-mm Diameter

E39 bulbs are primarily used in North America while E40 bulbs are popular in Europe. Bulbs with these bases can be used interchangeably as there is only a 1-millimeter difference in base size. These powerful bulbs have high light output and are used to replace HID bulbs in industrial fixtures, such as high-bay warehouse lights, parking lot lights, canopy lights, and wall packs. LED bulbs with these bases typically have a cylindrical shape like ED and BT HID bulbs. Because they resemble an ear of corn, they are called corn

Common bulbs with E39/E40 bases:

PAR (parabolic aluminized reflector) bulbs: PAR20, PAR38, PAR40

Blown tubular bulbs: BT37, BT56

Elliptical dome bulbs: ED17, ED28, ED37