Types of Lamp Fittings

The ‘cap’ or ‘base’ provides an electrical connection to the lamp and ensures the lamp is held in the correct position. It is essential to know the cap type to identify the lamp. Below we have listed the most popular fittings; if you can not find the type you are looking for or have any further questions please do not hesitate to call our sales team on 01462 490066 and we will be happy to advise you.

Watch our video guide to some of the most popular lamp fittings

Bayonet Caps

Bayonet caps are mainly used in Great Britain and are distinctive by their 'push and twist' action to install. There are many variations of a Bayonet Cap including some three pin versions known as B22d-3 found in new build homes and on some high pressure mercury lamps for industrial use.

Please note measurements are taken across the diameter of the bottom of the cap, not including pins.

Name Product Code/Stock Reference Diameter Diagram Image Description/Use Description
Bayonet Cap (BC) B22d 22mm B22d Diagram B22d Image Found in a range of applications, especially domestic
Small Bayonet Cap - double contact (SBC) Ba15d 15mm Ba15d Diagram Ba15d Image Found in a range of applications, especially domestic
Small Bayonet Cap - single contact (SBC) Ba15s 15mm Ba15s Diagram   Found in automotive/
machine applications
Miniature Bayonet Cap (MBC) Ba9s 9mm Ba9d Diagram   Found in a range of applications, especially industrial

Edison Screw Cap

Edison Screw Caps take their name from the inventor of the light bulb Thomas Edison and are universally used for a range of applications. The table below shows the most popular caps but other less common types are available including E11, E17, E26 and E39. It typically follows that the larger the cap the greater wattage and heat the lamp can withstand.

Please note measurements are taken across the diameter of the bottom of the cap.

Name Product Code/Stock Reference Diameter Diagram Image Description/Use Description
Lilliput Edison Screw (LES) E5 5mm E5 Diagram   Small decorative applications and indicator buttons
Miniature Edison Screw (MES) E10 10mm E10 Diagram   Often found in industrial applications
Candelabra Edison Screw (CES) E12 12mm E12 Diagram   An American cap but often used in Europe especially in candle shaped lamps
Small Edison Screw (SES) E14 14mm E14 Diagram E14 Image Commonly found in a range of domestic applications
Edison Screw (ES) E27 27mm E27 Diagram E27 Image This is the most popular Edison Screw cap and is found in a vast range of applications
Giant Edison Screw (GES) E40 40mm E40 Diagram   Commonly used in commercial 250w+ applications

Tip: It can be difficult to measure exactly the diameter of a cap, especially to the nearest mm, so it is useful to remember that CES fittings are distinctive by their three crests (twists in the fitting), all other Edison Screw fittings have four.

Fluorescent Tubes

Fluorescent tubes typically have two pins at either end but there are exceptions to the rule such as the T12 mono pin. Knowing the pin spacing and wattage of a fluorescent tube is enough to identify the lamp type.

Fluorescent Tube Type Product Code/Stock Reference Distance between pins Diagram Image
T4 (13mm) G5 5mm   T4 Diagram
T5 (16mm) G5 5mm T5 Diagram  
T8 (26mm) G13 13mm T8 Diagram T8 Image
T12 (38mm) G13 13mm T12 Diagram  

Architectural and Strip Light

Architectural lamps either have one main centre contact or two at either end. Strip Lights, often used as picture lights, have two contacts at either end.

Please note the diameter given is the measurement across the bottom of the cap.

Product Code/Stock Reference Diameter Diagram Image Description/Use Description
S12 12mm S12 Diagram S12 Image Two peg fittings at either end of the lamp
S14d 14mm S14d Diagram S14d Image One double oval contact in the middle of the lamp
S14s 14mm S14s Diagram S14s Image Two single oval contacts at either end of the lamp
S15 15mm     Found on strip lights. Two S15 contacts at either end of the lamp

Halogen Capsules

Halogen capsules are found in halogen adaptors where the components are: adaptor base – replaceable capsule – decorative cover. This type of lighting is commonly used in domestic environments.

Linear halogen capsules are frequently used in floodlights and have an R7 cap at either end of the lamp.

Product Code/Stock Reference Distance between pins Diagram Image Description/Use Description
G4 4mm G4 Diagram   Used in low voltage display applications
GY6.35 6.35mm GY6.35 Diagram   Used in low voltage display applications
G9 9mm G9 Diagram   Used in 240v mains applications
R7 7mm R7 Diagram   Typically found at either end of linear halogen capsules. Used in floodlights and up-lighters

Halogen and LED

GU fittings typically have two pins and are commonly found on halogen and more recently on LEDs. It follows that the larger the cap the great the wattage and heat the lamp can withstand. Therefore, GU4 and GU5.3 fittings are commonly found on low voltage/wattage lamps and often have a 'push fit' action. GU10 fittings are distinctive by their 'twist and lock' fitting action and are common in domestic applications.

The table below shows the more popular of these fittings; however we stock lamps in many other sizes and types including GY9.5, G22 and Gx38q.

Product Code/Stock Reference Distance between pins Diagram Image Description/Use Description
GU4 4mm GU4 Diagram   Used in spot lighting; both halogen and LED
GU5.3 5.3mm GU5.3 Diagram   Used in spot lighting; both halogen and LED
GU6.35 6.35mm GU6.35 Diagram   Used in spot lighting; both halogen and LED
GU10 10mm GU10 Diagram   Used in spot lighting; both halogen and LED

Compact Fluorescents (CFL)

Fittings for single, double, triple and quadruple turn compact fluorescents vary greatly and can be hideously complex to identify. The table below shows the most popular fittings available for particular types of CFL. We also stock a variety of three pin and special compact fluorescent fittings which our sales team will be happy to advise you with.

Lamp Company Part Code Product Code/Stock Reference Image Description/Use Description
PLC 2 pin 10 and 13w = G24d-1
18w = G24d-2
26w = G24d-3
PLC 2 pin Diagram Commonly found in commercial applications and some domestic energy saving fixtures
PLC 4 pin 10 and 13w = G24q-1
18w = G24q-2
26w = G24q-3
PLC 4 pin Diagram Commonly found in commercial applications and some domestic energy saving fixtures
PLL 4 pin 2G11 PLL 4 pin Diagram Commonly found in commercial applications and some domestic energy saving fixtures
PLT 2 pin 13w = GX24d-1
18w = GX24d-2
26w = GX24d-3
PLT 2 pin Diagram Commonly found in commercial applications and some domestic energy saving fixtures
PLT 4 pin 13w = GX24q-1
18w = GX24q-2
26, 32 and 42w = GX24q-3
PLT 4 pin Diagram Commonly found in commercial applications and some domestic energy saving fixtures
PLS 2 pin 5, 7, 9,11w = G23 PLS 2 pin Diagram Commonly found in commercial applications and some domestic energy saving fixtures
PLS 4 pin 5, 7, 9,11w = 2G7 PLS 4 pin Diagram Commonly found in commercial applications and some domestic energy saving fixtures

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