Guide to Light Fittings, Caps and Bases

What Are the Different Types of Light Bulb Fittings, Caps and Bases?

When replacing a light bulb, choosing the correct light bulb fitting, cap, ou base is just as important as selecting the right brightness or colour temperature.

O cap (also called the base) is the part of the bulb that connects to the light fitting. It provides the electrical connection while securely holding the bulb in place. Since different fixtures are designed for specific bulb types, manufacturers have developed a wide variety of light bulb bases to ensure only compatible lamps can be installed safely.

Whether you’re replacing a household bulb, a spotlight, or an LED tube, this guide explains the most common light bulb fittings, caps, and bases to help you find the right replacement.

Bayonet Cap

Bayonet caps are easy to recognize thanks to their push-and-twist locking mechanism. They remain popular in the UK, Austrália, New Zealand, and several other countries because they are secure, reliable, and simple to install.

BC B22 (Bayonet Cap)

Diâmetro: 22mm

Pin-to-Pin Diameter: 27mm

Height: 26mm

O BC B22, also known simply as B22, is the standard bayonet cap used in many household light fixtures. It features two locating pins that lock into the socket with a short twist.

Common applications include:

• Ceiling lights
• Table lamps
• Floor lamps
• Luzes de parede
• Decorative fixtures

Because of its durability and ease of installation, B22 remains one of the most widely used light bulb fittings.

SBC B15 (Small Bayonet Cap)

Diâmetro: 15mm

Pin-to-Pin Diameter: 17mm

Height: 26mm

De forma similar, o SBC B15 (Small Bayonet Cap) works in the same way as a B22 but is smaller in diameter.

It is commonly found in:

• Iluminação decorativa
• Arandelas de parede
• Iluminação de eletrodomésticos
• Small table lamps

Although most B15 bulbs operate on mains voltage, some specialist versions are designed for low-voltage applications.

Other Bayonet Variants

In addition to B22 and B15, several specialist bayonet fittings are available, incluindo:

• B22d-3 – Often used in Fireglow and industrial mercury lamps
• BY22d – Commonly used for low-pressure sodium (SOX) iluminação

Edison Screw Cap

Unlike bayonet fittings, Parafuso Edison (ES) caps screw directly into the socket. Named after Thomas Edison, they are now the most widely used light bulb bases worldwide.

ES E27

Diâmetro: 27mm

Height: 26mm

O E27 Edison Screw is the standard screw fitting throughout Europe, Ásia, Austrália, and many other regions.

No entanto, it is often confused with E26. Although the difference is only 1mm, the two bases are designed for different electrical systems.

• E27: 220–240 V
• E26: 110–120V (América do Norte)

Always check both the fitting size and operating voltage before purchasing a replacement bulb.

SES E14 (Small Edison Screw)

Diâmetro: 14mm

Height: 26mm

For smaller fixtures, o E14 Small Edison Screw is the preferred choice.

You’ll typically find E14 bulbs in:

• Lustres
• Luzes de parede
• Decorative pendant lights
• Iluminação de eletrodomésticos
• Iluminação de destaque

Graças ao seu tamanho compacto, E14 is especially popular for decorative LED filament bulbs.

Common Edison Screw Sizes

Capsule Lamps

Compared with standard bulbs, capsule lamps are much smaller and use two metal pins instead of a screw or bayonet fitting.

The model number simply refers to the distance between the two pins, making it easy to identify the correct bulb.

This design also prevents bulbs with different voltages from being installed in the wrong fixture.

G9 Base

Espaçamento entre pinos: 9mm

O G9 fitting is designed specifically for 220–240V mains voltage.

You’ll commonly see G9 bulbs used in:

• Luzes de parede
• Decorative pendant lights
• Lustres
• Iluminação sob o gabinete

Hoje, LED G9 bulbs are widely available and provide an energy-efficient replacement for traditional halogen capsules.

G4 Base

Espaçamento entre pinos: 4mm

By comparison, o G4 fitting operates on 12V and requires a compatible transformer or LED driver.

G4 bulbs are frequently used in:

• Cabinet lighting
• Display lighting
• Landscape lighting
• RV and marine lighting

GY6.35 Base

Espaçamento entre pinos: 6.35mm

O GY6.35 capsule is another low-voltage fitting designed for 12V or 24V systems.

It is commonly installed in:

• Iluminação de tarefas
• Candeeiros de mesa
• Display cabinets
• Iluminação de destaque

Felizmente, LED versions are available for all these capsule bases, making upgrades simple while significantly reducing energy consumption.

Linear Halogen

R7s Fitting

Cap Diameter: 7mm

Bulb Length: 78mm or 117mm

Unlike capsule lamps, R7s linear bulbs have contacts at both ends.

They are widely used in:

• Floodlights
• Security lights
• Work lights
• Uplighters

When replacing an R7s bulb, always match:

• Comprimento
• Potência
• Tensão

This ensures proper performance and safe operation.

Halogen and LED Spotlights

Spotlight bulbs are identified by the distance between their pins and the locking mechanism. Consequentemente, different spotlight bases are not interchangeable.

GU10

Tipo: Twist & Lock

Espaçamento entre pinos: 10mm

Operating directly from 220–240V mains power, o GU10 is the most common spotlight fitting used in residential and commercial lighting.

Nowadays, LED GU10 bulbs are available in various:

• Wattages
• Beam angles
• Colour temperatures
• Brightness levels

making them ideal replacements for halogen spotlights.

GU5.3 / MR16

Tipo: Push Fit

Espaçamento entre pinos: 5.3mm

Unlike GU10 bulbs, MR16 (GU5.3) spotlights require 12V power supplied by a transformer or LED driver.

They are commonly installed in:

• Kitchen lighting
• Display lighting
• Retail lighting
• Iluminação de destaque

GZ10

À primeira vista, o GZ10 looks almost identical to a GU10.

No entanto, there is one important difference.

The GZ10 uses a dichroic reflector, which directs heat backwards rather than forwards. Como resultado, the base has a square profile that prevents it from being installed in fixtures not designed to handle the additional heat.

Compatibilidade

• ✅ GU10 → fits GU10 and many GZ10 fittings
• ❌ GZ10 → should not be installed in GU10-only fixtures

Fluorescent Tubes and LED Tubes

Both fluorescent and LED tubes use two-pin caps at each end. No entanto, different tube diameters require different base types.

G13 / P8

Tube Diameter: 25mm

Espaçamento entre pinos: 13mm

O G13 fitting is the industry standard for T8 LED e tubos fluorescentes.

After inserting the tube, simply rotate it to lock it into place.

The same fitting is also used on:

• T10 tubes
• T12 tubes

G5 / T5

Tube Diameter: 16mm

Espaçamento entre pinos: 5mm

Enquanto isso, G5 fittings are designed for slimmer T5 tubes.

These compact tubes are widely used in:

• Escritórios
• Retail displays
• Iluminação sob o gabinete
• Iluminação comercial

The same cap is also found on some T4 fluorescent tubes.

Considerações Finais

Para concluir, identifying the correct light bulb fitting, cap, ou base is essential before purchasing a replacement bulb.

Whether your fixture uses a B22 bayonet, E27 Edison Screw, E14, G9, GU10, MR16, R7s, ou G13 fitting, selecting the correct base ensures a safe installation and optimal performance.

Finalmente, if you’re replacing an older incandescent, halogen, or fluorescent lamp, consider upgrading to an LED equivalent with the same fitting. Not only will you enjoy lower energy consumption, but you’ll also benefit from a longer lifespan, reduced maintenance, and improved lighting efficiency.