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What is the difference between E26, E27 and A19?

Posted by Sales Team on

Shoppers of LED Light bulbs often confuse the specifications for base type (E26 or E27) and bulb shape (A19). 

Base Type

E26 E27 LED Bulb Base

Screw in bulbs use a base called an Edison Screw or ES base. This base was developed by Thomas Edison for the first light bulbs and is still in use today.

There are four commonly used thread size groups for lamps:

  1. Candelabra: E12 North America, E11 in Europe
  2. Intermediate: E17 North America, E14 (Small ES, SES) in Europe
  3. Medium or standard: E26 (MES) in North America, E27 (ES) in Europe
  4. Mogul: E39 North America, E40 (Goliath ES) in Europe.

The number following the E indicates the size in mm of the external thread screw. Thus a E26 has a 26 mm base diameter. 

You may see low cost LED bulbs using an E27 base on eBay and Amazon from foreign suppliers. While these technically will work in E26 bases, this is usually a sure indication that the bulb was not strictly designed for the US market and this bulb may lack a proper North American, UL or ETL safety certification and therefore should be avoided. 

Bulb Shape

Now that we have learned that E26 and E27 are terms used to describe the type of base used what does A19 or bulbs with an A designation mean?

A type describes a bulb that has a pear-like shape. The number that follows the "A" within the A series indicates the width of the bulb in one-eighth inch units or in millimeters.

The most commonly used A-series light bulb type is the A19 bulb which is 2 38 inches (60 mm) wide at its widest point and approximately 4 38 inches (110 mm) in length. This is the classic shape that most people are used to when shopping for a "Light Bulb". You can use this handy image below to identify the size of your A Shaped bulb:


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25 comments

  • Thank you for this short, straight to the point, informative article. I just bought and installed my first light fixture that uses Edison bulbs, and I never knew how little I know about all the new types of bulbs on the market now. When I was younger (many decades ago!) the only thing you needed was a buck in your pocket to buy a 4 pack of GE bulbs, and know what wattage bulb you wanted. Now, you need to read up on lumens, wattage, color hue, and make a small investment in light bulbs. I’ve read 30 articles trying to figure out what type of bulb I should invest in. This article made it easy and clear for me on how to decide what type of bulb I need.

    Matt Ponteri on
  • Excellent read. I was confused on what bulb I should buy a while ago. This read made it clear. Thank you.

    Thanga Prakash on
  • GOOD man or rather good sales team! You guys kept it KISS and really did great on teaching the basics in a fast, clear way. You just earned a life customer there

    Maga guy on
  • thank you. good clarity about A17, as seen in American stores, being the pear shaped bulb.

    Lincoln Fong on
  • After reading many articles to learn the differences between bulbs, I wish this would have been the first one I’d read. This one is like having a school book explain the basic principles of a bulb. The illustration is the key. Now a mental picture of an “I got it” light bulb will light up in my head and I will remember that image. Thanks for the lesson!

    Jeannette G. on

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