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The overview of lamp holders and useful information.

The spectrum of bases and corresponding lamp holders is almost as large as the choice of lamps themselves. The confusing range extends from the classic screw base to the pin base and bayonet base to the socket base. There are retrofit bases for modern lamps such as LEDs, which make them suitable for older versions.

Only a manageable proportion of these lamp holder types is more widespread in practice. When choosing the lamp holder, pay attention to the exact designation. With a comprehensive overview of lamp holders, you can get an overview of their use in different types of lamps.

Types of the lamp holder

Due to the variety of luminaries for different areas of application and furnishing styles, there are a large number of different sockets and bases. But don’t worry: you will never see many of them in everyday life. The following list is therefore only an excerpt from common and some less common sockets and bases.

The base and socket are terms that contain a certain risk of confusion in an overview of the lamp base.

Sockets refer to a component on the lamp holder. It holds the lamp and makes contact.

The base corresponds to the lower part of the lamp. This part is used to establish contact with the lamp.

The base represents the electrical and mechanical contact points. So for the proper functioning of the lamp, the base and socket must be exactly coordinated.

You can differentiate lamp holders into different categories depending on the type of attachment:


The widespread screw bases are the first standardized base types. They create a simple screw connection with a thread using the socket. 

Their designation follows the Exx scheme, where xx stands for the number (E14, E27). The number indicates the outer diameter of the base in millimeters. The E pays tribute to the inventor Thomas Edison who built the first light bulb.

Pin base

Pin bases follow the type designations of the Gx or GUx diagram. The abbreviation G stands for the original material of the lamp body: glass.

The optional U is used for sockets that have a transverse groove on both sides. The x stands for the respective distance between the pins. There are two springs in the socket, which fix the lamp or snap it into place.

Pin bases were originally developed to avoid license fees for the patented screw bases or Edison bases.

Bayonet base

Bayonet bases or Swan bases (after the inventor Joseph Wilson Swan) consist of a sheet metal cylinder with two holding devices, the so-called holding lugs.

The lamp holder has corresponding recesses for the retaining lugs.

According to the principle of a bayonet lock, the cylinder is attached to the socket by turning it. 

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The retaining lugs are often staggered or of different sizes to ensure correct polarity.

Retrofit base

So-called retrofit sockets are types of sockets that are compatible with older sockets.

The term is particularly common for modern LED lamps, which can also be used in older lights.

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Manufacturers support the changeover or retrofitting of LED lamps by offering LED lamps for almost all areas of application.

Retrofit bases take current standards into account and make LEDs suitable as replacements for halogen bulbs, fluorescent tubes, and numerous other illuminants.

Tube Base

The base of fluorescent tubes or LED tubes is generally referred to as a tube base. The respective tube diameter is standardized and follows the standard DIN EN 60061: 2012-07. 

The designations of the bases follow the scheme Tx. T stands for an abbreviation for the tube. The x stands for the number after the T, which indicates the diameter. Different diameters sometimes come with identical bases. 

This ensures that, for example, T8 lamps are compatible with the versions of older T12 lamps. Today, T8 and T5 tube bases, in particular, are widely used. 

Sleeve base

Sleeve bases are directly related to the line lamps. Bulbs equipped with a socket base were originally classic light bulbs that had a filament in an elongated sleeve. 

This type of base is typically attached to the side of the lamp and is inserted into the socket via a plug connection. The names of these bases follow the scheme of the Sxxx structure. 

The S indicates the type of socket, xx for the distance between the sleeves and the last x for the number of contacts. S14d (d for “double”, ie two contacts) and S14s (s for “single”, ie one contact) are common.

Information about common Lamp holders

Lamp holders have specific names, each of which are characterized by precise properties and differ from others. The designation gives conclusions about the base types (e.g. screw base or bayonet base) as well as other properties, e.g. size or the number of pins.

E14 base

The widely used socket E14 is intended for the so-called candle holder. The designation “candle base” already indicates the original area of ​​application. E14 lamps are most common for chandeliers.

This is because the typical shape of an E14 lamp is the candle shape, which is particularly effective in chandeliers.

The base is also popular in desk and wall lamps.

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The E14 base is one of the screw bases. The designation E14 stands for the screw thread on the one hand and the diameter of 14 millimeters on the other. It is reminiscent of an E27 base, which is similar in function and technology.

Luminaries with E14 sockets can be easily fitted with LED bulbs with E14 bases in addition to incandescent and energy-saving lamps.

E27 base

In lamp holders, the base type E27 is perhaps the best known.

Lamps with an E27 base have the screw thread already known from the Edison light bulb.

The areas of application are the same as those of the classic light bulb and include numerous types of lamps.

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This base is also popular in LED lamps. The designation E27 denotes the screw thread and the diameter of 27 millimeters.

E27 bases are reminiscent of the smaller (E14) and larger (E40) relatives in the field of screw bases.

The E27 base is the typical base of a conventional light bulb. 

E40 base

The E40 base corresponds to the E27 base in terms of its design but has a larger base diameter.

Illuminants with this base are often used in industrial production halls or lighting technology on stages.

Commercial use is more common than private use. They have a particularly high level of brightness and common for illumination of large areas.

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Therefore, you can see their use in the parking lot and street lighting.

The base E40 belongs to the screw bases and has a thread diameter of 40 millimeters.

G9 base

G9 is a base type that was originally common for halogen spotlights. The high-voltage socket pins embedded in glass are typical of this socket. These usually have a characteristic loop shape. 

In the case of LED lamps, however, these bases are framed in plastic and have a pin shape. Typical applications are in-ceiling and wall lights. Hanging and table lamps can also be equipped with corresponding sockets. 

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The base designation G9 is sometimes also given alternatively as GU9. This type of base belongs to the pin bases. Base and socket are standardized: the distance between the contact pins is always 9 mm.

This makes it easy to replace a G9 halogen lamp with a G9 LED lamp – with the corresponding advantages.

GU10 base

The base type GU10 is characterized by a BiPin foot. Similar to G9 bases, GU10 lamps are used primarily in ceiling lights. It belongs to the pin bases. 

The abbreviation GU10 indicates several aspects. 

  • G stands for the original material used (glass). 
  • U stands for the type of mechanical hold in the socket. 
  • The number 10 indicates the pin spacing.

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The pins themselves are parallel metal pins. Their diameter is 5 millimeters at the end of the pin.

The GU10 socket is mostly fit with high-voltage halogen reflector lamps. The usual form of luminaries was that of a single-lamp or multi-lamp spotlight, mostly on the ceiling. The GU10 base is a bayonet base.

G4 base

Bulb types with the G4 base form also belong to widespread lamps for a wide range of applications.

They are often used in desk lamps. Furthermore, they are often used as lighting for extractor hoods and in mobile homes.

They belong to the pin bases.

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G4 sockets are characterized by a pin spacing of 4 millimeters. 

The socket pins themselves have a diameter of 0.65 to 0.75 millimeters in this design and differ, among other things, from the socket type GU4.

GU4 base

GU4 sockets are similar to the G4 sockets. They were originally mainly installed in halogen lamps.

There are also comparable LED lamp bases for LEDs.

GU4 lamp holders are used, for example, in the table and wall lights or RV and motorhome interior lighting.

This is also a pin base.

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As with G4, the distance between the pins is also 4 millimeters, only the pin diameter is somewhat larger at 0.95 to 1.05 mm.

GU5.3 base

GU5.3 is also an original halogen lamp base. This type of lamp base is used in particular in conjunction with the MR16 design, which describes the diameter (16/8 ″, approx. 50 mm) of the reflector. 

This pin base is installed in both low-voltage halogen lamps and LED lamps.

In the household, lamps with this base are often used as basic lighting, for example in the dining room or living room. 

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The number 5.3 describes the distance between the socket pins, namely 5.3 mm.

This is also the difference to the GU4 sockets with a pin spacing of only 4 millimeters.

R7s base

R7s bases belong to the types of bases that are essentially connected with rod lamps.

The base is widely used for halogen lamps.

Halogen flashlights are very energy consuming lamps, for which LED replacement is now also available.

Rod lamps exist in different lengths and power levels.

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Floodlights, ceiling wash lights as well as outdoor and parking lot lighting is typical areas of application. 

The base has cup-shaped contacts on both sides and is suitable for spring clip sockets.

G53 base

The G53 base is also a widely used base for halogen and LED spotlights. It has two pins as contact parts. 

The designation G53 results from the distance between these pins: 53 mm.

This base is usually installed in lamps with type AR111, ie a reflector diameter of 111 mm. 

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The G53 AR111 reflector lamp is common in shops, as shop window lighting or at exhibitions.

Since the halogen version is extremely energy-consuming, it is often worth switching to LED reflector lamps.

GY6.35 base

The base designation GY6.35 indicates the distance between the pins of 6.35 millimeters.

This pin base is for low-voltage halogen lamps but is now also available as an LED version.

These lamps are common as furniture or showcase lighting, but also in restaurants or hotels.

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The diameter of the two-socket pins is between 1.2 and 1.3 millimeters.

This differs from the similar G6.35 base with a smaller distance between 0.95 and 1.05 mm).

B15 base

In lamp holders, lamp types with a bayonet base are also important. Type B15 bases have a twist lock. This ensures a secure hold, even in the event of vibrations. 

Areas of application are, for example, machine and vehicle lighting.

B15 bases have a sleeve diameter of 15 millimeters. The B15d design is particularly common. The B15 base belongs to the bayonet base, also known as the Swan base.

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In the USA and France, bayonet bases are much more widespread than in Europe and are also common in the home. 

B15 bases exist in different designs. The d in the well-known design B15d stands for double and denotes the two-foot connections. 

B15s, on the other hand, has an only one-foot connector (single). If there is an A behind the B, for example in the BA15d design, this stands for the automotive application area.