Light bulbs have a variety of fitting types (also called bases or caps) which connect the bulb with the light fitting to ensure a secure fit and to conduct electricity to the bulb.
Light bulbs are also available in different shapes to provide the best fit and look with light fittings.
This guide explores the most common bulb fitting types and shapes to help you identify the bulb you need.
LED Light Bulb Bases/ Fitting Types
There are 2 common types of bulb bases used in UK light fittings:
Edison Screw (ES)
As the name suggests, Edison Screw bulbs simply screw into light fixtures and are named after Thomas Edison, who was the US inventor usually credited with the invention of the light bulb (although there is some debate about this).
These bulbs start with the letter E and a number which relates to the diameter of the base (in mm). The 2 popular ones in the UK are:
| E27 Base | E14 Base |
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| Base Diameter: 27 mm | Base Diameter: 14 mm |
| Also known as Edison Screw, ES | Also known as Small Edison Screw, SES |
2) Bayonet
Bayonet cap bulbs use a simple push and twist motion to fit.
B22 and B15 are 2-pin bayonet bulbs popular in the UK. The BC3 bulb is a newer, specialist bayonet bulb which has 3 pins in a T-shape:
| B22 Base | B15 Base | BC3 Base |
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| Diameter: 22 mm | Diameter: 15 mm | Diameter: 22 mm |
| Also known as: Bayonet Cap, BC, 2-pin Bayonet | Also known as: Small Bayonet Cap, SBC | Also known as: 3-Pin Bayonet |
Light Bulb Shapes
There is a wide selection of bulb shapes to choose from, ensuring you can find the perfect fit and aesthetic for your light fixtures.
Let's explore the most common shapes:
Standard Shape
UK Bulb Code: A60 (and close variations such as A55), where the number refers to the width (in mm) of the widest part of the bulb.
Common length: Approx. 100-110mm long.*
Candle
Candle-shaped bulbs are often used in chandeliers, wall sconces and other decorative light fittings.
Common UK Bulb codes: B35, C35, where the widest part of the bulb measures 35mm.
Common length: Approx. 88-100mm*
Globe/ Golf Ball
As the name suggests, golf-ball bulbs are smaller and round-shaped. These fit well in smaller light fittings such as desk and table lamps. Also known as mini-globe bulbs.
UK Bulb code: G45, where the widest part of the bulb measures 45mm.
Common length: Approx. 74-78 mm*
Larger globe bulbs are available for larger, open feature light fittings (codes G80, G95 or G125, with common length: 115 – 170 mm)
Pear
Pear-shaped bulbs are longer (and slightly wider) than standard bulbs and are most often used in decorative, open light fittings.
UK Bulb codes: ST64 (where the widest part of the bulb is 64mm) or ST58 (where the widest part of the bulb is 58mm)
Common length: Approx. 130-140 mm*
*You can find the exact dimensions of all our bulbs in the datasheets on our website.
Bulb shapes are given codes which consist of a letter representing the bulb series, followed by a number which correlates to the widest part of the bulb (in mm).
Please note, you may sometimes see different codes which relate to the non-UK/ USA shape codes and which show the widest part of the bulb in inches. Some common examples are shown below:
| UK/EU Bulb Shape Code | Equivalent USA/ China Bulb Shape Code |
| A60 (standard) | A19 |
| A55 (standard) | A17 |
| C35 (candle) | B11 |
Further information
You can find information on the base cap, shape code and dimensions for all our bulbs in the datasheets available on our website.
If you’re looking for more tips on buying the right light bulb, check out our buying guide for LED bulbs, which provides lots of useful information, including about brightness and colour temperature.
Please get in touch if you have any questions about our ECO bulbs.
