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Light Fitting Caps Explained: Types, Sizes & Compatibility Guide
Understanding Light Fitting Caps
Light fitting caps—also known as bulb bases or lamp sockets—are standardised connectors that allow light bulbs to attach securely to fixtures. Choosing the correct cap type is essential for compatibility, safety, and performance. While bulbs may look similar, their bases can differ significantly in size, shape, and voltage requirements.
This guide covers the most common light fitting caps used in homes and commercial spaces, explaining where each type is typically found and how to identify the right one for your fixture.
Quick Reference: Common Light Fitting Caps
E26 / E27 – Edison Screw
26–27mm diameter · 120–240V · Used in ceiling lights, pendants, table and floor lamps
E14 – Small Edison Screw
14mm diameter · 220–240V · Chandeliers, wall lights, decorative lamps
GU10 – Twist & Lock Spot
10mm pin spacing · 220–240V · Downlights, spotlights, track lighting
GU5.3 / MR16 – Low Voltage Spot
5.3mm pin spacing · 12V · Accent lighting, display and cabinet lighting
G9 – Capsule Pin
9mm pin spacing · 220–240V · Decorative fittings, under-cabinet lights
B22 – Bayonet Cap
22mm diameter · 220–240V · Common in UK & AU ceiling fixtures and lamps
E26 / E27 (Edison Screw)
E26 (US) and E27 (EU) are among the most widely used caps worldwide. Featuring a screw-in design, they’re compatible with incandescent, LED, and CFL bulbs.
They’re found in everything from pendant lights and ceiling fittings to table and floor lamps. Their simple screw mechanism makes them easy to replace and highly versatile.
E14 (Small Edison Screw)
The E14 is a smaller version of the Edison screw, commonly used in decorative and compact fixtures such as chandeliers, wall sconces, and bedside lamps.
Its reduced size allows designers to create more delicate luminaires while maintaining the familiar screw-in convenience.
GU10
GU10 bulbs use a twist-and-lock base and are most often found in spotlights and recessed downlights. They operate at mains voltage and are popular in kitchens, bathrooms, and commercial interiors.
The secure locking mechanism makes them reliable for directional and high-intensity lighting.
GU5.3 / MR16
GU5.3 (often called MR16) is a low-voltage pin base commonly used in accent and display lighting. These bulbs typically operate at 12V via a transformer.
They’re widely used in retail displays, cabinets, and landscape lighting where controlled, focused light is needed.
G9
The G9 is a compact two-pin cap used for capsule-style bulbs. It’s common in decorative fittings, under-cabinet lights, and modern luminaires where space is limited.
Its small size allows for sleek designs while still delivering effective illumination.
B22 (Bayonet Cap)
The B22 bayonet cap is widely used in the UK, Australia, and several other regions. It features a push-and-twist locking system that holds the bulb firmly in place.
Common in ceiling lights and lamps, B22 fittings are valued for their secure connection and regional standardisation.
Conculsion
Choosing the correct light fitting cap ensures safety, performance, and compatibility. Whether you’re replacing a single bulb or planning a full lighting scheme, understanding these base types makes selecting the right bulb simple and reliable.
Browse Light Bulbs by Fitting Type →
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