Buying Guides – Light Fitting Types – Traditional Light Bulbs

Light Fitting Types, Traditional Light Bulbs

When we think of a light bulb, we traditionally referred to an incandescent or tungsten filament lamp with a round sphere at one end or a candle lamp that is long and thin. Nowadays we talk more about LED: LED bulbs are more energy efficient, cheaper to run and better for the environment. Most of these lights have round metal caps with either a screw or bayonet type fitting.

At Lyco we sell a wide range of these traditional light bulbs and we understand that the types that are available are not as simple as they once were. With this in mind we have put together a quick guide to fitting types and traditional light bulbs…

Standard Fittings & Effects

The types of lamp available with the above mentioned screw and bayonet caps have broadened greatly in recent years to include LED. With traditional caps you get great flexibility and a wide choice of lighting effects.

Bayonet & Screw Caps

There are two different types of bayonet cap – standard and small. Standard is by far the most popular and is perhaps the most common light bulb of all in the UK. Screw caps are available in four common sizes – Micro (MES), Small (SES), Standard (ES) and Goliath or Giant (GES).

In addition, many other LED light bulb fittings are also available, such as striplights which have a tube shape not dissimilar to fluorescent lighting.


The bayonet cap type fitting (BC) is perhaps the most well known lamp fitting in the UK today. Invented towards the end of the nineteenth century and ultilising a mechanism originally developed for bayonet rifles, the BC consists of a spring and two contacts with bayonet mounts on either side.

To fit, simply depress the lamp into its holder, twist under the lugs and the bayonet mounts are retained by the springs, thus ensuring optimum contact – the simple push and twist most of us are familiar with.

Size Variations

The most common sizes of bayonet cap fittings are BC or B22d, (where 22 refers to the diameter in mm of the lamp base) and small bayonet cap – SBC (or B15d). For insulation and safety purposes such fitting typically feature a plastic or metal skirt.

Common Uses

It is most common to find bayonet fittings in pendant lights, batten holders, wall and ceiling lights designed for domestic use. BC fittings can be enclosed in some very decorative luminaires and traditionally incandescent tungsten filament lamps are used. Nowadays, there are also low energy lamps with bayonet caps, which mean you can keep your existing fittings and reduce damage to the environment at the same time.


Another very popular fitting type for domestic lighting purposes is the screw cap – invented by Thomas Edison in 1909 and trademarked under Mazda.

Using the metal screw as one contact and a single base as the other, the lamp simply screws into the fitting. Contact is made when the lamp screw is almost home, thus making the screw part both the physical and electrical contact that makes the circuit.

Screw Cap Reliability

The screw fitting can be thought of as easier to maintain, particularly as there are no springs involved which can fail over time. However, there is a small drawback in that it is possible to cross-thread.

Size Variations

The most common types of screw cap in the UK are the eponymous ES or Edison Screw E27, (where the number relates to the diameter of the screw), SES or Small Edison Screw (E14), Giant or Goliath Edison Screw GES (E40) and MES or Miniature or Micro Edison Screw (E10).

To find your ideal bulb by shape or cap try our Light Bulb Finder

Domestic Light Fittings

Although ES is the most popular choice for domestic fittings, there are now many more SES lamps available. This is because retailers are sourcing light fittings from Europe and the US; locations where this fitting is far more common.

Giant Edison Screw fittings are generally not suitable for domestic use and more suited to specialist street lamps and industrial fittings. MES fittings are less common and ideal for use in very small or battery powered light fittings.

Other Light Bulbs

In addition to the common bulb fitting types there are many other less common types available, typically for more specialist use. Whichever fitting you choose, remember that you should always replace like for like.


Striplights are a form of incandescent lighting with unique double-ended sprung fittings. They are commonly used for picture lights, but other applications have tended to be superseded by linear fluorescent tubes as they are more reliable.

Heater & Catering Bulbs

Catering light bulbs come in variety of types, from doubled ended (striplight / linear halogen fittings) to edison screw and bayonet fittings.

PAR Lamp Fittings

Some PAR lamps have a screw terminal for better electrical contact, while others have a GX160 2 pin cap with ceramic base. The fittings are usually porcelain to take the high heat output.

Professional Light Fittings

For high intensity luminaries (for film, stage and TV use for example), professional fittings such as the T and A types are most commonly used. Caps are 2 pin, being either GY9.5 or P28S.

If you are looking for traditional bulbs, why not take a look at our extensive range of incandescent light bulbs?
Alternatively, our full range of light bulbs includes energy saving and LED options to suit all your needs.

Looking for more news, inspiration or advice? Try our Lighting Advice section.

Where Next?

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