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Light Bulb Base Sizes Explained

Each lighting fixture has its own requirements of the light bulb base size and shape, and your bulb will work well only when it's perfectly compatible with the fixture socket. In this case, whenever you go to purchase a new light bulb, firstly check out its package to learn about the bulb base size it has. And to help you actually know what light bulb base size you need for different situations and fixtures, we've briefly covered the common light bulb base types below.

How do I know what light bulb base sizes?
What are light bulb base types common?

How do I know what light bulb base sizes?

Having trouble in knowing what light bulb base the replacement should have? All you should do is to measure your light bulb base before purchase, as it helps you to sure that the new bulb you select is going to fit into your fixture. Normally, a bulb with a screw base or bayonet base measures the diameter of the base, while a pin base measures the spacing between two pins. All kinds of light bulb bases are measured in millimeters. For further understanding, take the e26 bulb base as an example, it's a typical screw base, "26" refers to its base diameter of 26 mm.

What are light bulb base types common?

These days, light bulbs are designed with a variety of bases to compatible with different kinds of sockets and lighting fixtures. Among them, there are four most common base types, including Edison screw base, bayonet base, bi-pin base, twist and lock base. Below are the details about them.

Edison Screw Base

Edison screw bases are the most common base types, as they are also used in the most popular LED bulbs today. That's why LED bulbs are a great alternative to traditional incandescent bulbs. The letter "E" stands for Edison screw-in style, after the great inventor, and the number for the base diameter. Among them, E26 base and E12 base are the most familliar bulb bases to us, which are also called medium base and candelabra base. The others are E11, E14, E39, E40, etc. Note that most Edison bases are single-contact bases, but a few are double-contact bases that add a "d" to the end, such as the E26d, which is commonly used for three-way bulbs.

enlightenedE26 Bulbenlightened

With a base diameter of 26mm, they are the most commonly used light bulbs in North America. When you type E26 to search for light bulbs online, you can see that there are many LED light bulbs with different functions, like dusk to dawn lights, yellow bug lights, smart lights, etc. These are the most poplar LED light bulbs that can meet your different lighting needs with low power.

Technical Details Comparison of LOHAS E26 LED Bulbs

smart bulb

e26 dusk to dawn light bulb

e26 yellow led bulb

e26 smart retrofit downlight

e26 led daylight bulb
Price $21.99/2 Pack $25.99/4 Pack $19.99/4 Pack $25.99/Pack $29.99/4 Pack
Lumen 450LM 500LM 450LM 680LM 2500LM
(Replacement Watt)
(60W Equivalent)
(40W Equivalent)
(40W Equivalent)
(65W Equivalent)
(150 - 200W Equivalent)
Light Color RGB &
Cool White
Daylight White Orange Yellow RGB &
Tunable White
Daylight White
Color Temperature 2700K-6000K 5000K 2000K 2000K-9000K 50000K
Shape A19 A19 A15 Round Candle
Key Functions Controlled by Voice and APP Auto Turn ON or OFF Provide sufficient illumination without attracting bugs Decoration
Controlled by Voice and APP
Light comes on instantly when turned on
Dimmable × × ×

enlightenedE12 Bulbenlightened

Compared to the e26 bulb, the bulb base size of an e12 light bulb is smaller. Many of these e12 light bulbs are designed to mimic candle flames or in other shapes, so they are usually used in decorative lighting such as chandeliers, pendant lights, wall lights.

Technical Details Comparison of LOHAS E12 Light Bulbs

smart bulb

e12 color changing light bulb

e12 filament vintage light bulb

e12 filament vintage light bulb

e12 decorative cylindrical bulb
Price $26.99/2 Pack $29.99/2 Pack $22.99/6 Pack $29.99/6 Pack $18.99/3 Pack
Lumen 450LM 810LM 400LM 600LM 1100LM
(Replacement Watt)
(40W Equivalent)
(60W Equivalent)
(40W Equivalent)
(60W Equivalent)
(100W Equivalent)
Light Color RGB &
Cool White
Tunable White
Warm White Warm White Warm White
Color Temperature 2700K-6000K 2700K-9000K 2700K 2700K 2700K
Shape Candle A19 ST48
Beam angle:
Candle Candle
Key Functions Controlled by Voice and APP Controlled by Voice and APP Decoration Decoration Decoration
Dimmable × ×

Bayonet Base

Bayonet base, got its name from the same push and twist action used by soldiers to mount bayonets on their rifles. Most bayonet light bulbs have a pin on either side of the base that locks into the socket when twisted. Commonly used are B22, B15 base, the number refers to the diameter of the base. Note that some bayonet bases are single contact (SC), while others are double contact (DC). This means that there are one or two contact points for electrical connection.

Bi-pin Base

Another common base type is bi-pin base, traditionally used for fluorescent bulbs and LED bulbs. Each bi-pin base light bulb has two pins that stick out of the base, and connect the bulb to the voltage, then the electrical current flows through the pins into the bulb to emit light. All bi-pin bases are designated with a letter letter “G” followed by a number. “G” dates back to the original light bulb made of glass, and the number indicates the distance between two pins in millimeters. Common ones are G4 bulbs and G9 bulbs. In some cases, the numbers are followed by letters that indicate how many pins the light bulb has, “S”: single-pin; “D”: double-pin; “T”: triple-pin; “Q”: quadruple-pin.

Twist And Lock Base

You may have heard of GU10 base and GU24 base, exactly, they are typically twist and lock bases. There are also two pins protruding from the base, sort of like the bi-pin base. To install these bulbs you need to insert the pins into the holes in the socket, then twist and lock them into place. Available in CFL and LED light bulbs. The number following the letter indicates the distance between the two pins.

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By knowing the type and size of the bulb base, you can ensure that you get the right bulb you need. By the way, LED light bulb sockets and bases are manufactured to the same standards as halogen, incandescent, CFL and other traditional lights. Replacing your existing light bulbs with LEDs is a great option with lower energy consumption and more environmental protection.