A Guide To Understanding Light Bulb Base Types And Sizes

Pandemic has brought a lot of changes to almost all of us. With many good and bad impacts on our lives, another thing that the pandemic has changed for most of us is the shopping experience. Most of the urban population has moved to shop online rather than in stores. From apparel to appliances, we rely on e-commerce stores more than ever.

For instance, my friend had to replace a few light bulbs as some of her LED lights changed colors due to prolonged use. Instead of buying the lights from the store, she decided to order them online. But she got stuck when she couldn’t figure out which bulb would fit in her light bulb fixtures. As a result, she called me and asked, ‘how do I know what base my light bulb is?’ While explaining to her how to measure light bulb bases and different types of light bulb bases, I decided to put my research into words and write this article.

Each light bulb has a specific code that tells about the type and size of the bulb base. If you are trying to decipher your light bulb base type, the first thing you need to identify is the type of the bulb connector. Examine whether your light bulb has a screw-type connector that threads around the base or a pin-type connector with one or two points of contact at the base. The next step is to measure the diameter of the base in millimeters. 

This article will discuss different types of light bulb bases in detail. We will also learn how to measure the size of the light bulb base.

Light Bulb Base Types

These days light bulbs come with a variety of bases. Every light bulb has a code printed on its base, which is a combination of one or two letters along with a number. It is noteworthy that this code is not the same code that describes the size and shape of a light bulb. The code printed on the base describes the type and size of the bulb base and helps you understand whether a particular bulb is compatible with your light bulb fixture or not. 

Depending on the connector that connects the light bulb to the fixture, there are two main types of light bulb bases.

Light Bulb Base Types

You can identify your bulb base type by observing the already installed bulb, examining the bulb socket, or reading the bulb code on the socket if printed.

How To Measure Light Bulb Base?

How To Measure Light Bulb Base?

The number in the code of the light bulb base represents the size of the bulb base. The measurement of an Edison screw bulb base is done differently than the bi-pin bulb base. The size of the Edison screw bulb base is the diameter of the wide part of the base. In comparison, the size of a bi-pin bulb base is the distance between the two pins of pins. Note that the length of the pins is not the number represented in the code, but the code of the bulb base varies as the length of the pins varies. The application of different pin sizes may be different.

Various Light Bulb Base Codes

Depending upon the light bulb socket type and the measurement of the light bulb base, various codes are allotted to the bulb bases. While the codes of the bulb bases are almost the same across the world, the bulb base varies in North America and Europe due to the voltage difference. 

Various bulb base codes of Edison screw base and Bi-pin base are discussed below.

Edison Screw Base

Edison Screw Base

The Edison screw base was developed by Thomas Elva Edison when he invented the first light bulb and is the most commonly used base in most light bulbs. The light bulb base has a right-hand threaded metal base that screws into the matching threaded sockets in the fixture. The light bulb base code for these light bulbs starts with the letter E and is followed by a number that describes the diameter of the base. Some of the commonly used Edison screw bases are E12, E26, E27, E39, etc. E26 is the standard light bulb base size in the US, whereas E27 is the standard light bulb base size in Europe.  

While most Edison screw bases are single-contact bases, a few of them are double-contact bases. The nomenclature of double contact bases has an added letter d. For example, the E26d bulb base is commonly used in three-way bulbs.

This section of the article will discuss various Edison screw bases. The light bulb base size chart given below gives a comparative depiction of various bulb bases with an Edison screw.

Edison Screw Base

E10

E10

The E10 bulb base, also referred to as MES, i.e., Miniature Edison Screw or Mini Screw, is the Edison screw base with a base diameter of 10 millimeters. The bulb base is commonly used in old chandeliers. Hence, the light bulbs designed to fit in the E10 base are more decorative in appearance. The bulb base is also used in miniature lamp applications and indicating panels.

E11

E11

The E11 bulb base is the Edison screw bulb base with a base diameter of 11 millimeters. The bulb base is commonly installed in Mini Candelabra bulb fittings which are becoming popular in many new chandeliers and ceiling fans. Mini Candelabra are slightly smaller in size as compared to Candelabra bulbs. To read more about ceiling fan light bulbs, you may read the article I wrote recently.

E12

E12

E12 bulb base, as the name suggests, is an Edison screw bulb base with a base diameter of 12 millimeters. E12 light bulb bases are commonly called Candelabra bulbs as these bases are most widely used with the candelabra bulbs whose shape resembles the flame of a candle. Since they are pretty popular for their decorative and retro look, these bulbs are very commonly used in chandeliers and ceiling fans.

E14

E14

The E14 bulb base, or Small Edison Screw, is an Edison screw base with a base diameter of 14 millimeters. The bulb base is popularly known as the European bulb base as it is a common bulb base used across Europe. The bulb base is found in many small light fittings like bedroom lights and chandelier lights, and many shapes of bulbs are available with an E14 base.

E17

E17

Like candelabra bulbs are the bulbs with E12 bases, intermediate bulbs are the bulbs with E17 bases. That means Intermediate bulbs are light bulbs with an Edison screw and a base diameter of 17 inches. These light bulbs are larger in size than the E12 bulbs and are commonly used in ceiling fans, microwave lights, refrigerator lights, etc.   

E26

E26

E26 is the bulb base with an Edison screw and a base diameter of 26 millimeters. An E26 base can be used in various light bulbs of different shapes and sizes and is a standard bulb base in countries like the USA, Japan, Taiwan, South Korea, etc., where the standard voltage is 120V. The bulb base is commonly referred to as the medium bulb base.

E27

E27

E27 bulb base often referred to as the medium bulb base like the E26 bulb base, is an Edison screw bulb with a base diameter of 27 millimeters. The bulb base is the standard bulb base in Europe and other countries, with a standard voltage of 220V. The base is popular, fitting in a range of domestic lighting. 

While E26 and E27 bulbs are mechanically similar and appear interchangeable but are not, from an electrical safety point of view, E26 offers lesser insulation and protection against short circuits and electrical fires. Also, E26 bulbs are designed for the market, which primarily uses 120V AC, whereas E27 lamps are designed for other markets which use 240V AC. You may be able to use an E27 bulb in the E26 socket, but using E26 bulbs in E27 sockets is not advised.

E39/E40

E39/E40

E39 and E40 bulbs are the Edison screw bulb bases with a base diameter of 39 millimeters and 40 millimeters, respectively. These bulb bases are commonly known as Mogul bulb bases. While the E39 bulb base is primarily used in the US, Canada, Japan, Taiwan, etc., the E40 bulb base is popular in Europe. These powerful bulb bases have high light output and are used for indoor industrial lighting. Light bulbs with these bases typically have an extended-arbitrary shape with a cylindrical neck.

EX39

EX39

EX39 is an Edison screw bulb with a base diameter of 39 millimeters and an extended tip at the bottom. An EX39 bulb base is equipped with a longer tip at the screw base, which acts as a protective shield and makes it a perfect high-intensity light bulb base to be used in an open setting. An EX39 light bulb base can operate with both an E39 and an EX39 light bulb fixture. However, a light bulb with an E39 base can only operate with an E39 fixture and will not operate with an EX39 fixture.

Bi-Pin Base

A bi-pin base is a light bulb fitting included in the International Electronic Commission standard. The letter G dates back to the original light bulb made of glass, and the number describes the distance between two pins in millimeters. 

These bases can be identified by two pin-like contact points at the bottom. The pins connect the bulb to the voltage, and the electrical current flows through the pins into the light bulb to emit light. Some low-power bulbs, also called mini bi-pins, have the pins closer to each other, preventing them from being replaced by bulbs that are too high in power. This prevents fire due to generating excessive heat. These bulb bases are often used on small incandescent light bulbs.

In this section of the article, we will talk about various bi-pin light bulb bases. The light bulb base size chart given below gives a comparative depiction of various bi-pin bulb bases.

Bi-Pin Base

G4

G4

The number 4 in the name G4 indicates the center-to-center distance between the two pins of the bulb base, in millimeters. Hence, the G4 light bulb base is a bi-pin bulb base with 4 millimeters distance between the two pins. The bulb base comes in 6, 12, or 24 Volts. The G4 bulb base is ideal for decorative fixtures, cabinet lighting, projector lamps, dental lamps, and caravan lamps.

GU4

GU4

Like the G4 light bulb base, even the GU4 bulb base both have two pins and a pin spacing of 4 millimeters. Hence, both the bulb bases are bi-pin bulbs for low-power bulbs. The difference between the two bulb bases is that the GU4 type base has a pair of grooves on the sides to hold the lamp in place.

GU5.3

GU5.3

The GU5.3 light bulb base is a bi-pin base with two pins 5.3 millimeters apart. The bulb base types are ideal for spotlights, track lighting, recessed ceiling lights, etc. GU5.3 is a typical fitting for MR16 lighting. 

GU8/GY8

GU8/GY8

Both GU8 and GY8 light bulb bases are bi-pin bases with 8 millimeters distance between the pins. The difference between GU8 and GY8 base is the pin length. While the pin length of the GU8 bulb base is 8 millimeters, the pin length of the GY8 bulb base is 8.5 millimeters.

The pin thickness of both the bases is the same, i.e., 1 millimeter.

Though the pin length for both the bases is different, for most applications, the bases can be interchanged.

GY8.6

GY8.6

The GY 8.6 bulb base is a bi-pin bulb base with an 8.6 millimeters distance between the pins. The bulb base is commonly used for halogen and LED lights and is suitable for ceiling lights, desk lamps, side table lamps, etc.

G9

G9

A G9 bulb base is a paperclip end bulb base with two pins 9 millimeters apart. The G9 light bulb base is a high-quality bulb base with an efficient capsule that does not require a transformer. The bulb base is suitable for 240V applications and is suitable for ceiling lights, desk lamps, and side table lamps. G9 bulb base is available with halogens and LED lighting, with dimmable options available.

G12

The G12 bulb base has two paper clip pins 12 millimeters apart and a ceramic base as the contact point. These bulb bases are commonly used in stadium lights, flood lights, architectural lighting, and photography and film lighting equipment. G12 bulb base is most often found on high-intensity discharge lighting and other metal halide lighting.

FAQs

Q1. What are the different light bulb bases?

Answer – There are different light bulb bases used for various lights. The two most common bulb bases are the Edison screw base and the Bi-pin base.

Q2. What is a bulb base code? Is it different from the bulb code?

Answer – A light bulb base code is a combination of letters and numbers wherein the letter represents the type of bulb base, and the number represents the code size of the bulb base. A bulb base code tells us about the shape and size of the metallic bulb base that is installed into the socket, but the bulb code represents the shape and size of the glass bulb. 

Q3. How do I know what base my light bulb is?

Answer – Identify the code of your bulb base by observing the type of the base and measuring its size. A bulb base with a screw is an Edison screw bulb base, and the bulb base with two pins is a bi-pin bulb base. The size of the Edison screw bulb base is the diameter of the wide part of the base. In contrast, the size of a bi-pin bulb base is the distance between the two pins of pins.

Q4. Is E26 a standard bulb base across the world?

Answer – E26 is the standard bulb base in North America and other countries like Japan, Taiwan, etc., where the standard voltage is 120V, whereas the E27 bulb base is the standard light bulb base size in Europe and other countries with a standard voltage of 220V. 

Q5. Can I use the E26 bulb in the E27 fixture?

Answer – E26 bulbs are designed for the market, which primarily uses 120V AC, whereas E27 lamps are designed for other markets which use 240V AC. You may be able to use an E27 bulb in the E26 socket, but using E26 bulbs in E27 sockets is not advised as E26 light bulbs offer lesser insulation and protection against short circuits and electrical fires. 

Conclusion

The terminology for bulb base can be challenging to understand if you are unfamiliar with it. But with immense innovation in the lighting industry and various kinds of bulbs and bulb bases surfacing around in the market, it is essential to have a guide to refer to in case you need to find out about light bulb bases. I hope this article serves that purpose for you. 
If you found the article helpful in understanding the light bulb socket types and codes, write to me in the comment section. You may also post your queries in the same section, and I will try my best to solve them for you.

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