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

L1 lamp cap

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.

G24d

G24d ('d' is for double pin) PL lamps are available with either a double or triple turn tube.

Double turn bulbs usually have a square lamp base (G24d) and triple turn usually have a hexagonal lamp base (GX24d).

PL 2 pin

G24q ('q' is for quad pin) PL lamps are available with either a double or triple turn tube.

Double turn bulbs have a square lamp base (G24q) and triple turn have a hexagonal lamp base (GX24q).

PL 2 pin

Rectangular-based 2G11 and 2G7 4 pin lamps with a single turn tube.

PL 2 pin

Rectangular-based G23 2 pin lamps with a single turn tube.

Other lamp caps

G9 Halogen capsule

G9 cap

G9 bulbs are available at various wattages, and are only now available in clear glass or LED version. 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, hence G9.

G4 lamp cap

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.

Due to 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. The pins are 4mm apart, hence G4.

GU10 lamp cap

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.

GU10 lamp cap

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.

BC - Bayonet cap

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.

SBC - Small bayonet cap

Also known as SBC and B15

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

ES - Edison screw cap

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

SES - Small Edison screw cap

Also known as SES and E14

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