Common bulb types

This page shows some of the common lamp caps that are in use today, and provides some basic information about each one. This isn't an extensive list of all the available lamp caps, but it shows the most common ones.

Dedicated low energy lamp caps

L1 - dedicated low energy

The L1 lamp cap is used a various shapes and sizes of bulb, its based on GU10, with important difference of a hole in the middle of the lamp. The lamp holder has a corresponding pin that fits into this hole, and prevents a standard GU10 lamp being used.

The L1 cap is used on self ballasted compact fluorescent bulbs.

PL - 2 pin - dedicated low energy

Also known as GX23 or G23.

There are various versions of this shape of 2 pin lamp depending on the wattage of the bulb. It's important to make sure that you have correct version as the different versions are different shapes. The wrong version will not physically fit.

PL bulbs have the ballast separate from the tube.

 

PL - 4 pin - dedicated low energy

Also known as G24.

There are various versions of this shape of this lamp cap. Some variations only have 2 pins.

It's important to make sure that you have correct version as the different versions are different shapes. The wrong version will not physically fit. The variations are described by a 'q' or 'd' number. e.g. G24-q2. If you have a light fitting that uses this type of connection, it will be marked to show exactly which type of bulb you need. If you are removing a failed bulb it too will be marked to show what it is.

The light fitting contains the ballast required for these bulbs.

Other lamp caps

G9 Halogen capsule

G9 bulbs are available at various wattages, are have clear or frosted glass. They are often used on small decorative light fittings where a high light output is required.

Some manufactures add a ceramic base to the lamp. The pins are 9mm apart.

G4 Halogen capsule

G4 bulbs are the smallest type of commonly used bulb, the pins are just 4mm apart.They are low voltage bulbs usually requiring 6v, 12v or 24v.

Because of their tiny size, they are often used in intricate light fittings, where style is more important than light output. Light fittings that use G4 bulbs often use many bulbs to compensate for the relatively low light output.

GU10

GU10 bulbs are often spot lights, used in recessed downlighters. They are mains voltage bulbs running at 230v. GU10 is one of the safest types of mains voltage lamp holder as all the electrical live parts are concealed even when the bulb is removed.

Although the GU10 cap is similar to the L1 low energy cap, GU10 bulbs can not be used in L1 light fittings.

Various wattages and styles of bulbs are available.

GU5.3

Also known as MR16

GU5.3 bulbs are low voltage usually running at 12v. the pins are 5.3mm apart.

The most common use for this lamp cap is for spot lights, in recessed or decorative light fitting.

Bayonet

Also known as BC and B22

The bayonet cap is not the safest of caps as the lamp holder has bare connection that you can touch if the bulb is removed.

Replacement low energy lamps are available with BC caps.

Small bayonet

Also known as SBC and B15

This is the same as the larger Bayonet cap, only smaller.

Screw

Also known as ES and E27

The screw cap is not the safest of caps as the lamp holder has bare connection that you can touch if the bulb is removed.

Replacement low energy lamps are available with ES caps

Small screw

Also known as SES and E14

This is the same as the larger Bayonet cap, only smaller.