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Understanding Light Bulb Screw Bases


With hundreds of different types of bulb bases on the market today, and the ever-growing list of LED Light Bulbs, it can be a challenge ensuring that the right bulb is chosen.

Add to the fact that there are different styles and light bulb base sizes, even for the same bulb shapes, and it can quickly become an overwhelming process.

Take the four most common types of bulb bases, for instance. There are screw, bayonet, wedge, and bi-pin bases to account for, all of which are used in different applications and work using different sockets.

In this article we will be discussing light bulb screw bases which are also referred to as Edison bulb bases, named after their inventor, Thomas Edison.

Light bulb screw bases are commonly used in North America and Europe, and are identified with the letter “E” followed by a set of numbers indicating the width of the base in millimeters, and are available in a wide range of sizes.

E26 and E27 Medium Base

E26 bulb bases are most commonly used in North America while E27 bulbs are more common in Europe. Bulbs with these bases can be used almost interchangeably, as there is only a 1mm difference in base size. These are typically used in general lighting applications, such as ceiling lights, lamps, can lighting, and vanity lights.

Common Bulbs with E26 / E27 Bases

A-Series Bulbs

BR (bulged reflector) Series bulbs

Globe-Shaped bulbs

PAR (parabolic aluminized reflector) Series bulbs

E12 Candelabra Base

E39 / EX39 / E40 Mogul Base

E14 European Base

E14 bulb bases are most 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.

Some common bulb shapes that use E14 bases include:

  • Smaller A-Series bulbs

  • Small T-Series bulbs

  • Smaller Globe-Shaped bulbs

  • Candle and Marquee bulbs

E17 Intermediate Base

Similar to E12 Candelabra bases, intermediate bases are used in decorative applications and also used for appliance lighting, such as for microwave lights, refrigerator lights, and range hood lights, and can also be found in ceiling fan light fixtures.

Some common bulb shapes that use E17 bases include:

  • Smaller A-Series bulbs

  • Small T-Series bulbs

  • Smaller Globe-Shaped bulbs

  • Candle and Marquee bulbs

For a complete list of the different Bulb Bases and Shapes, please feel free to check out our Bulb Shape and Base Guide!

If you have any additional questions regarding LED Light Bulbs or if you would like to provide us with any additional feedback, we always have our ears open to new input and suggestions, and we enjoy learning from others and sharing knowledge. Please feel free to contact us today for a complimentary quote on your lighting project or simply to provide some additional input by giving a call at (813)-649-8899 or simply emailing us at

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  • Michael Tomas