Light Bulb Fitting Guide

Bayonet cap bulbs use a twist and lock motion to secure into the fitting. They’re highly versatile and commonly used in residential properties, and are one of the most widely used types of fittings.

There are also micro bayonet caps (MBC) which are more commonly used in industrial environments, and Ba15d caps which are used in vehicles or mains voltage lamps.

Tube caps are generally used in large commercial areas such as offices because they’re energy efficient and don’t produce much heat. They typically have two pins at either end to slot into the contacts in the light fitting to transfer electricity, unless they are called ‘mono pins’ – with just a single contact.

Tube caps also last a long time, are more cost-effective, and some have fly-killing properties.

They are referred to as T caps followed by a number, but this number doesn’t usually represent the distance between the pins or size of the cap. Instead, you may see the cap referred to as a G cap followed by the distance between the pins – such as a G13 fitting.

Architectural caps have either one main contact or two at either end, while strip lights always have two contacts at either end. Generally they’re used for picture lights or shaving mirrors.

You’ll find architectural and strip light caps in a small, bayonet style cap making for easy installation without the need for twisting which can be difficult in tight spaces with small bulbs.

Strip and architectural lights are referred to as S caps followed by a number which represents the diameter of the base.

Halogen capsules are referred to as G caps followed by a number which represents the distance in millimetres between the two pins.

From September 2021, most halogen light bulbs were phased out because they are less environmentally friendly than LED alternatives – the ones that remain are generally the lower-voltage decorative bulbs which have less of a negative environment impact.

They’re mainly used in domestic environments, spotlights and lamps. They’re generally found in halogen adaptors where you have an adaptor base, the replaceable capsule, and a decorative cover. You may find halogen capsules in small, decorative lights such as Christmas lights.

Compact fluorescent lights (CFL) are commonly used for commercial applications and some energy-saving fixtures in residential buildings.

Both two and four pin CFL caps are simple to install – just hold the bulb and push the pins into the fixture.

You’ll find 2-pin and 4-pin CFL caps available. 2 pin CFLs use magnetic ballasts to hold the bulb in place, whereas 4-pin CFLs use electronic ballasts. Electronic ballasts work at much higher frequency than magnetic alternatives so they’re less likely to flicker or make buzzing sounds.