A Complete Guide to Light Bulb Fittings, Caps, and Bases in the UK

When it comes to lighting your home or workspace, understanding the different types of light bulb fittings, caps, or bases is essential. With so many options available, it can be overwhelming to know which bulb fits your fixture. In this comprehensive guide, we’ll explore the most common light bulb fittings in the UK, including BC, ES, GES, MES, SES, SBC, GU, GY, and T-type caps. By the end, you’ll be equipped with the knowledge to choose the right bulb for your needs.

Choosing the Right Light Bulb Fitting

Understanding light bulb fittings, caps, and bases is crucial for ensuring compatibility with your fixtures and achieving the desired lighting effect. Whether you’re replacing a bulb or designing a new lighting scheme, this guide has covered the most common types in the UK, including:

BC (B22) and SBC (B15): Bayonet fittings for general and compact lighting.

ES (E27), GES (E40), MES (E10), and SES (E14): Screw fittings for versatile and decorative lighting.

GU4, GU5.3, GU10, G9, and GY6.35: Bi-pin and twist-and-lock fittings for directional and specialised lighting.

T4, T5, and T8: Tubular fittings for even, energy-efficient illumination.

By matching the right fitting to your fixture, you can ensure optimal performance and longevity for your lighting.

1. BC - B22 Bayonet Cap: The UK’s Most Common Fitting

The B22 Bayonet Cap (BC) is the standard light bulb fitting in the UK. It features a push-and-twist mechanism, making it easy to install and replace. The "22" refers to the diameter of the base in millimeters.

Common Uses: Ceiling lights, table lamps, and pendant lights.

Popular Bulb Types: LED, incandescent, and CFL bulbs.

Why Choose B22? It’s widely available and compatible with most UK light fixtures.

2. ES - E27 Edison Screw: The Global Standard

The E27 Edison Screw (ES) is one of the most popular light bulb fittings worldwide. The "E" stands for Edison, and "27" indicates the diameter of the screw base in millimeters.

Common Uses: Floor lamps, chandeliers, and outdoor lighting.

Popular Bulb Types: LED, halogen, and vintage-style bulbs.

Why Choose E27? It’s versatile and works with a wide range of decorative and functional lighting.

3. GES - E40 Giant Edison Screw: For Industrial and High-Wattage Applications

The E40 Giant Edison Screw (GES) is designed for high-wattage and industrial lighting. It’s much larger than the standard E27 fitting, with a 40mm diameter base.

Common Uses: Streetlights, stadium lighting, and industrial fixtures.

Popular Bulb Types: High-intensity discharge (HID) and LED bulbs.

Why Choose E40? It’s ideal for heavy-duty applications requiring powerful illumination.

4. MES - E10 Miniature Edison Screw: Small but Mighty

The E10 Miniature Edison Screw (MES) is a tiny fitting often used in small appliances and decorative lighting. The base measures just 10mm in diameter.

Common Uses: Fairy lights, bike lights, and model train sets.

Popular Bulb Types: Miniature incandescent and LED bulbs.

Why Choose E10? It’s perfect for compact and low-voltage applications.

6. SBC - B15 Small Bayonet Cap: Compact and Convenient

The B15 Small Bayonet Cap (SBC) is a smaller version of the B22 fitting, with a 15mm diameter base. It’s less common than the B22 but still widely used in the UK.

Common Uses: Small table lamps, appliances, and decorative lighting.

Popular Bulb Types: LED and incandescent bulbs.

Why Choose B15? It’s compact and fits smaller fixtures seamlessly.

5. SES - E14 Small Edison Screw: The Candle Bulb Fitting

The E14 Small Edison Screw (SES) is commonly used for smaller light fixtures. The base has a 14mm diameter and is often found in decorative bulbs.

Common Uses: Chandeliers, wall sconces, and bedside lamps.

Popular Bulb Types: Candle-shaped bulbs, LED, and halogen.

Why Choose E14? It’s ideal for adding a touch of elegance to your lighting.

7. GU4, GU5.3, and GU10: Bi-Pin and Twist-and-Lock Fittings

GU fittings are characterised by their two-pin or twist-and-lock design. The number after "GU" indicates the distance between the pins in millimeters.

GU4 (4mm Pin Spacing): Often used in low-voltage MR11 bulbs.

GU5.3 (5.3mm Pin Spacing): Commonly found in MR16 halogen and LED bulbs.

GU10 (10mm Pin Spacing): A twist-and-lock fitting used in spotlights and downlights.

Common Uses: Recessed lighting, track lighting, and kitchen spotlights.

Popular Bulb Types: LED and halogen bulbs.

Why Choose GU Fittings? They provide secure connections and are ideal for directional lighting.

8. G9 Caps: Compact and Versatile

The G9 fitting features two looped pins and is commonly used in small, compact bulbs.

Common Uses: Under-cabinet lighting, desk lamps, and decorative fixtures.

Popular Bulb Types: Halogen and LED capsules.

Why Choose G9? It’s space-saving and perfect for modern, sleek designs.

9. GY6.35 Caps: For Specialised Lighting

The GY6.35 fitting has two straight pins spaced 6.35mm apart. It’s often used in specialized lighting applications.

Common Uses: Projectors, medical equipment, and stage lighting.

Popular Bulb Types: Halogen and LED bulbs.

Why Choose GY6.35? It’s designed for precision and reliability in niche applications.

10. T4, T5, and T8: Tubular Bulb Fittings

T-type fittings are used for tubular fluorescent and LED bulbs. The number after "T" refers to the diameter of the tube in eighths of an inch.

T4 (12mm Diameter): Compact and energy-efficient.

T5 (16mm Diameter): Slim and bright, often used in modern fixtures.

T8 (25mm Diameter): The standard size for fluorescent tubes.

Common Uses: Office lighting, under-cabinet lighting, and garage fixtures.

Popular Bulb Types: Fluorescent and LED tubes.

Why Choose T-Type Bulbs? They provide even, widespread illumination and are energy-efficient.