Light bulb bases facilitate secure electrical and mechanical connections between the bulb and the fixture. Besides supplying power to light the bulb, these bases ensure that it’s securely fixed onto the lighting fixture to prevent it from toppling. The E-type bases are the most common options you’ll come across, but what does E mean?

The letter “E” in light bulb bases means Edison Screw, a standard light bulb base for residential and commercial lighting fixtures. These bases are suitable for sockets with a screw thread that screws into a matching threaded socket on light bulbs for a tight fit.

In the rest of this article, I’ll discuss the most popular light bulb base types. You’ll learn about suitable bulbs for each base, so keep reading!

The Origin of the Letter “E” in Light Bulb Bases

The E-type light bulb base is the most popular on the market, but why the letter “E?”

As mentioned, “E” stands for Edison Screw. However, where did this name come from?

Let’s explore!

The name “Edison” comes from Thomas Edison, the man credited with inventing the light bulb base.

An old photo of Thomas Edison
The “E” in light bulb bases is short for Edison, as in Thomas Edison.

Edison designed a screw base for use in his incandescent bulbs. This patented design became incredibly popular, leading to the widespread use of “E” bases for light bulbs worldwide.

Today, different E-type light bulb bases are available. Whenever you purchase a light bulb base, you must check it will work well with your bulb type and socket.

Classification of Edison Screw Bulb Bases

The following are the major classifications of Edison Screw bases based on their thread sizes:

● Candelabra

● Intermediate

● Medium or standard

● Mogul

Let’s now look at each of these classifications in detail.

Candelabra Edison Screw Bases

The candelabra is a small E-type base mainly used in low-wattage bulbs.

The E11 and E12 base types are the most commonly used candelabra base types. Bulbs with these bases are ideal for small lamps, nightlights, bathroom mirrors, and mini chandeliers.

In naming these bases, the letter “E” represents Edison Screw, while the number denotes diameter in millimeters.

an LED candelabra bulb sitting on a table with a black background
Candelabra or “candle bulbs” have a very small (typically E12) socket base to fit into small sockets in your household.

Therefore, the E11 base has a diameter of 11 millimeters, while the E12 has a diameter of 12 millimeters.

It’s worth mentioning that the base’s diameter corresponds to the size of the lamp holder. In this case, while the E11 version fits into an 11-millimeter socket, its E12 counterpart fits into a 12-millimeter socket.

In terms of prevalence, E12 is common in North America. On the other hand, the E11 base, also referred to as the mini candelabra, is common in Europe.

Besides the mentioned lamps, you can also use the candelabra E-type bases with the following bulbs:

● Christmas lights

● Restaurant pendant lights

● Ornamental lights

● Commercial and residential string lights

me holding up an e12 candelabra LED bulb with my bathroom light vanity fixture in the background
To show you an E12 socket base, I pulled this out of my bathroom vanity light fixture. You can tell it’s LED by those thin yellow tubes inside the bulb also. The label will tell the rest, like the Kelvin Temperature and wattage.

The common bulbs that use candelabra bases include:

Small globe-shaped bulbs: G14, G16, G50

Small tubular bulbs: T6, T8, T22

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

A simple way to identify candelabra light bulb bases is to look for bulbs with a candle flame shape. Alternatively, you can measure the base’s actual diameter using the procedure below:

  1. Hold the base in an upside-down position.
  2. Place a caliper at the top of the base and read its diameter.
  3. Repeat this process for all bases you want to identify.

Here’s a video that demonstrates how to identify the E12 candelabra bulb base:

Intermediate Edison Screw Bases

These E-type bases have a larger diameter than their candelabra counterparts. Moreover, they’re common in low to medium-wattage bulbs.

You can use intermediate E bases for decorative purposes such as wall sconces, restaurant pendant lights, marquee lights, and chandeliers.

They are also common in appliance bulbs such as ovens, fridges, microwaves, and televisions.

The E14 and E17 are the most common intermediate E bulb bases.

E14 Intermediate Base

The E14 intermediate base is the most common option in this category. Its diameter of 14 millimeters makes it larger than candelabra bases but smaller than the standard base size.

The E14 base type is commonly found in Europe and China. It’s suitable for chandeliers, wall sconces, Christmas lights, lamps, ornamental lights, restaurant pendant lights, night lights, and string lights.

The bulbs with E14 base types include:

Small tubular bulbs: T6, T8, T22

A-shaped bulbs: A15

Signal and marquee bulbs: S11

Small globe-shaped bulbs: G14, G16, G50

E17 Intermediate Base

As the name suggests, the E17 base has a diameter of 17 millimeters. This is typically larger than the common E12 base and smaller than the E26 base.

As with all E bases, you can identify this size by measuring its diameter with a caliper.

These bases are suitable for decorative light fixtures such as wall sconces, ceiling fans, and pendant lights. They are also used in appliance lightings like refrigerators and range hoods.

It’s worth noting that the E17 intermediate base is commonly used in North America.

Bulbs that use the E17 intermediate bases include:

Small tubular bulbs: T6, T8, T22

A-shaped bulbs: A15

Signal and Marquee bulbs: S11

Small globe-shaped bulbs: G14, G16, G50

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

Medium or Standard E-type Bases

These are the most popular light bulb bases. Bulbs with these bases are also the most popular in the market.

Medium or standard E-type bulb bases are suitable for general lighting fixtures such as ceiling, vanity, flood, and outdoor lights.

You’ll also find these bulbs in portable lamps like table and desk lamps, floor lamps, and night lights.

If you have can lights in your attic, check out this article on insulating and air sealing them for energy efficiency.

The most common standard E-type bases are the E26 and the E27. The good thing is that you can use these bases interchangeably since they have a diameter difference of only 1 millimeter.

The Medium E26 (MES) Base

The medium Edison Screw (MES) base has a diameter of 26 millimeters (approximately 1 inch) with a rating of 120 volts. This base type is common in North America and is used for general lighting.

An important point to note is that ‘E26″ doesn’t refer to the bulb’s shape, only the base. Therefore, when people say an “E26” bulb, they’re referring to any bulb that uses an E26 base for electrical contact and mounting.

An easy way to recognize an E26 bulb is by looking at the non-light-emitting side or the bottom. While doing so, you should see a metallic cap with approximately one-inch diameter screw threads.

an A15 and A19 bulb standing up next to each other
You’ll find E26 Edison bases to be the most popular for households. These are your typical light bulbs you can buy in almost any store.

Alternatively, you can look at the printing on the bulb’s base. In most cases, the bulb will have an “E26” label with its wattage equivalent.

The most common bulbs with E26 medium Edison screw (MES) bases include:

A-shaped bulbs: A15, A19, A21

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

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

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

Some advantages of E26 bases include the following:

● They are common, so it’s easy to find an appropriate lamp holder and bulb

● They are suitable for almost all types of light fixtures and lamps

● E26 bulbs generally have a longer lifespan than candelabra or intermediate base bulbs

The Standard E27 (ES) Base

E27 is the European standard for light bulb bases, replacing the old E26 base in Europe. The diameter of these bases is 27 millimeters (about an inch), with a rating of 220 volts.

Like the E26 base, E27 is suitable for general lamps or fixtures.

As I already mentioned, you can use the E26 and E27 bases interchangeably.

Therefore, if you’re using a lamp with an E27 base, you can easily replace it with an E26 without affecting the functionality and appearance of the light.

In addition, the E26 bulbs listed above are also compatible with E27 bases.

Mogul E-type Bases

These are the bases with the largest diameter. They are suitable for high-wattage bulbs like high-intensity discharge lamps, streetlights, reflector floodlights, and large decorative lamps.

The E39 (North America) and E40 (Europe) are the most common mogul E-type bases.

These bases have a diameter of 39 and 40 millimeters, respectively.

a forklift driving in a warehouse with metal halide light fixtures lighting up the aisle it's in
Mogul E-type bases have the biggest diameter, which can help you identify them. They have big diameters because they are made for the biggest fixtures, which almost mean they put out a ton of light.

There is also the EX39 bulb base in North America. The EX39 is a variation of the E39 bulb base, the only difference being that the former has a longer fitting tip at the screw base.

Another thing to note is that bulbs that use the EX39 base have protective shields, making them suitable for closed and open lighting fixtures.

Moreover, the EX39 bulbs will not work in E39 sockets and vice versa. Therefore, although you can use E39 and E40 bulb bases interchangeably, EX39 bulbs are incompatible with E39 and E40 sockets.

It’s important to note that the more wattage a bulb consumes, the more heat it generates. As a result, high-wattage bulbs require bases that can withstand high temperatures.

Mogul bulb bases are cast porcelain with good thermal conductivity and the ability to withstand high temperatures. Additionally, the threads have a coating meant to prevent corrosion.

Due to the above properties, Mogul bulb bases are suitable for high-energy bulbs with a rating of 250 to 1,000 watts.

According to the National Electrical Code, regular lamps that exceed 300 watts should not be used with medium or standard E-type bases.

Instead, these bulbs should be used with E39 or E40 bases for safety. Disobeying this guideline can be a safety hazard since the base can melt due to the high temperatures.

Some advantages of mogul bulb bases include the following:

● They can support high-wattage bulbs without overheating or incurring electrical damage

● They are suitable for outdoor lighting fixtures and lamps

● They are resistant to elements like water, dust, and corrosion, making them ideal for outdoor lighting

Expert Tip: Mogul types bases can be expensive depending on the wattage they can support. Therefore, you should refer to your bulb’s wattage before buying these bases. If the bulb’s wattage is 250, go for a 250-W Mogul base instead of the 300-W option to save some money.

Other E-Type Bulb Bases

Besides the above categories of E-bulb base types, there are other variations you’ll find in the market.

Here’s an overview of the various types.

E10 Bulb Base

These bases have a smaller diameter than the standard Candelaria versions. With a diameter of 10 millimeters, these bases are used for compact fluorescent lamps (CFLs) and miniature bulbs.

Usually, these bulbs take on a more decorative appearance suitable for chandeliers, nightlights, and holiday decor.

E5 Bulb Base (Midget)

This is the smallest of the E-type light bulb bases. It has a diameter of only 5 millimeters, making it extremely small. Therefore, the E5 base is ideal for low-wattage bulbs like nightlights and decorative ones.

Bulbs that use the E5 bulb base have very low brightness. Consequently, they’re not suitable for areas where brightness is vital. You can use them to set the mood in bedrooms and living rooms.

The table below summarizes the crucial points about E-type bulb bases:

Base CodeDiameterApplications
E55 mm (0.217 in)Indicator and decorative lights
E1010 mm (0.394 in)Bicycle lights and flashlights
E1111 mm (0.433 in)Chandeliers, night lights, decorative lighting
E1212 mm (0.472 in)Chandeliers, night lights, decorative lighting
E1414 mm (0.551 in)Chandeliers, wall sconces, Christmas lights, ornamental lighting
E1717 mm (0.669 in)Christmas lights, ornamental lighting, chandeliers, wall sconces
E2626 mm (1.024 in)Can lights, ceiling lights, vanity lights, flood lights
E2727 mm (1.063 in)Can lights, flood lights, ceiling lights, vanity lights
E3939 mm (1.535 in)High-intensity discharge lamps, streetlights, reflector flood lights
E4040 mm (1.575 in)High-intensity discharge lamps, streetlights, reflector flood lights

Table 1: E-type light bulb bases and their applications

Other Popular Light Bulb Bases

To this point, you know the ins and outs of E-type bulb bases. However, these are not the only types of bulb bases you’ll find on the market.

The other popular light bulb base types you’ll come across include these.

Bayonet Base

You might have heard soldiers use a push-and-twist action to mount bayonets on their rifles. Similarly, inserting bulbs with this base is a push-and-twist process, hence the name.

Bayonet bulb bases use a fastening mechanism with cylindrical male and receptor female sides.

The male side has radial pins, while the female has matching L-shaped slots. The pins slide into the L-shaped slots when you insert them into the socket.

A spring pushes the pins in until they click to keep the bulb securely in place.

Up-close shot of a car headlight
Car headlights and brake lights use bayonet bulb bases.

Bulbs with bayonet bases are standard in the automotive field. You’ll find them in car headlights, brake lights, and other lighting fixtures to meet the high demand for brightness.

There are two main types of bayonet bulb bases: B15 and B22.

B15 Bayonet Light Bulb Bases

The code “B15” illustrates the base name and diameter. The letter “B” denotes bayonet, and the number 15 indicates that the base has a diameter of 15 millimeters.

These bulb bases are popular in home light fixtures like table lamps and portable torches. They are also common in automotive applications, including headlights and tail lights.

Due to their small size, they are quite affordable, which is yet another reason for their popularity.

It’s worth mentioning that it can be challenging to find an appropriate bulb for a bayonet base due to their detailed coding. For instance, you may find a bulb coded as BY15 or BY15d.

To make it clear, the letter “Y” after “B” means “Yellow.” Thus, if you see “BY15” when looking for a suitable bulb, it’s ideal for a BY15 base, but it emits yellow light.

If you see the letter “A” after “B,” it means the bulb is suitable for automotive use.

Any small letter after the diameter size represents base contact. The most common letters for this purpose are “d” and “s.”

“d” means double contact socket while “s” means single contact socket.

B22 Bayonet Light Bulb Bases

Again, the letter “B” denotes bayonet, and the number 22 indicates a base diameter of 22 millimeters.

The most significant difference between this type and B15 is their size. Both have identical pins and slot mechanisms, so they use the same push-and-twist mounting approach mechanism.

Bulbs that use the B22 base have a similar coding mechanism to B15 bulbs. The only difference is that, due to the size, they usually have a code like BY22d or BY22s.

“B22d” means white light with a double contact of 22-millimeter diameter, while “BY22s” means yellow light with a single contact of 22-millimeter diameter.

Here are other bayonet base names and their suitable applications.

BA7s: Interior lighting for motor vehicles. An excellent example is the speedometer backlight.

BA9s: Sidelights

BA15s: Indicator, reversing, stop, daytime running, rear fog, and license plate lights.

BAU15s: Colored lights for indicators

BAY15d: Brake and rear lights

BA20s: Vehicle lights for places like railways

BA20d: Signal lamps

Besides automotive, bayonet bulb bases are ideal for ships, aircraft, devices, and machine lighting.

The bayonet lock eliminates connection loosening, making these bases effective in places prone to mechanical vibrations.

Bi-Pin Base

Bi-pin light bulb bases are common in fluorescent and LED bulbs.

As the name suggests, these bases have two pins sticking out from both sides. The pins connect the bulb to the voltage source, allowing electric currents to flow and emit light.

Moreover, these bases have a wedge facilitating direct connection to fluorescent bulbs.

As with the other bulb base types, you would expect that bi-pin bases have codes that start with “Bi.” However, this is not the case.

Bi-pin bases have a unique coding system. Usually, their codes start with the letter “G.” The letter “G” is an acronym for glass, the material used to make traditional light bulbs.

After the letter “G” comes a number that illustrates the distance between the two pins in millimeters.

Bi-pin bases are also popular with energy-saving fluorescent bulbs since they require less electricity than their traditional incandescent counterparts.

Check out this article for the four easy ways to tell if your bulbs are energy-efficient.

G4 and G9 are the typical light bulbs compatible with bi-pin bases. The bulbs may also have letters after the number to show the number of pins. These letters are:

S: Single pin

D: Double pin

T: Triple pin

Q: Quadruple pin

Twist and Lock Base

These are bulb bases that allow the twist and lock mechanism. All you have to do is insert the bulb into the socket, twist it until you hear a click, and lock it in place.

The two pins protruding from each side of the base permit the locking mechanism.

Twist and lock bases are usually found on CFL and LED light bulbs for residential use. They are ideal for long-term installation since they are less prone to vibrations, as with bayonet bases.

The main types of twist and lock bases are the GU10 and GU24 bases.

The distance between the pins in GU10 bases is 10 millimeters. These bases are common in garden, commercial, and track lighting applications.

An overhead shot of a garden with lights at night
Twist and lock lights are a common sight in gardens.

GU24 bases have the same pin configuration as GU10 bases but with a separation distance of 24 millimeters instead of 10 millimeters.

These bulbs are typically used in fluorescent lights for residential purposes like ceiling fixtures, recessed downlights, under-cabinet lights, and wall sconces.

If you’re looking for ceiling light fixtures, check out this article with the four best energy-efficient options on the market.

How to Choose the Right Light Bulb Base

Choosing the right base size for your bulb is crucial to facilitate the flow of electricity and mechanical connection.

Here is how to choose the right base size.

Consider the Screw Type

Light bulb bases come in two main screw types:

● Threaded screws

● Pin-based screws

Threaded base screws have a long cylindrical shape with internal threads that are either machined or molded. Some base screws have a knurled surface to allow for easier twisting.

On the other hand, pin-based light bulb bases have two pins sticking out from both sides.

Besides connecting the bulb to the voltage source, these pins act as a locking mechanism after twisting the bulb.

E-type bulb bases use threaded screws. Thus, they’re compatible with light sockets that also have threaded screws.

Pin-based bases are suitable for compact fluorescent lights and fluorescent tubes.

Consider the Diameter

Diameter comes in handy when looking for the right base size. For example, a light bulb base diameter is typically measured in millimeters (mm) or inches.

Most light bulb bases vary from 5 to 60 millimeters. The good thing is that these bases have labels that indicate the size.

Therefore, it’s up to you to consider the labels and choose one that will fit your bulbs.

Consider the Voltage

The voltage of your light bulb base depends on whether you’re using it for home, commercial, or industrial purposes. While most standard light bulbs have 120 voltage, others can be as high as 230 volts.

Hanging light bulbs at various distances with a soft amber glow
Use the voltage of your bulbs to choose the right base.

A base voltage of 120 volts is standard for residential use. However, suppose you decide to use a compact fluorescent light (CFL) for residential purposes.

In that case, it might have a higher voltage than the standard 120 volts.

What Will Happen If I Choose the Wrong Base Size?

If you choose the wrong light bulb base size, the bulb will not connect to the power source correctly. If the base size is too small, it won’t fit into the bulb. Otherwise, the bulb will be loose if the base is too large. A loosened bulb is at risk of falling off from the socket.

What’s more, you might end up damaging the bulb. For instance, a loose bulb might fall and break.

It can also cause injury to you or your property. Therefore, choosing the right light bulb base size is crucial.

Final Thoughts

There are different light bulb bases depending on the type of bulb you have. To choose the right light bulb base size, consider screw type, diameter, and voltage.

Doing so will ensure that your bulb connects to the power source appropriately and stays secure.

It’s advisable to consult a professional lighting expert if you need clarification on the right base size for your bulbs.

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