LED Bulbs and Lamp Types — GU10, B22, E27, E14 and SBC Lamp Caps for UK Electricians and DIYers

Swapping halogen and incandescent lamps for LED equivalents is one of the most common jobs on any domestic or commercial site. Get the cap type wrong, however, and the lamp will not fit the fitting — and a mismatch in wattage or colour temperature can cause complaints from customers. This guide covers the four lamp cap families used in virtually every UK property: GU10 spotlights, B22 bayonet-cap GLS lamps, E27 Edison-screw GLS lamps, and E14/SBC candle lamps. It explains what each cap looks like, which fittings it serves, how to select the right wattage and colour temperature, and which safety regulations apply.

The Four Main UK Lamp Cap Types

Every lamp cap is defined by its shape and pin spacing (for plug-in caps) or thread diameter (for screw caps). Understanding which cap a fitting uses before opening the packaging avoids unnecessary return trips.

GU10 — Twist-Lock Spotlight

The GU10 cap has two round pins with a 10 mm spacing and a twist-lock action: push the lamp into the holder and rotate 30° clockwise until it clicks. GU10 is the universal spotlight cap in UK domestic and retail fitouts, used in recessed fire-rated downlights, surface-mounted spotlights, and track lighting. The original 50W halogen GU10 runs hot enough to be a fire risk if touched or installed in an enclosed fitting; a 5–7W LED equivalent runs cool enough to handle immediately after switching off.

When to specify GU10: any fixed downlight or spotlight fitting, kitchen cabinet under-lighting, bathroom Zone 1/2 fittings rated IP65 (check fitting IP rating, not just the lamp), retail track lights. GU10 lamps are available in non-dimmable and dimmable variants — confirm which before purchasing if the circuit has a dimmer switch, as a non-dimmable LED on a leading-edge dimmer will flicker or fail prematurely.

Colour temperature selection: 2700K (warm white) for domestic living spaces and bedrooms; 4000K (cool white) for kitchens, garages, and commercial spaces; 6500K (daylight) for workshops and photography. The colour rendering index (CRI) should be Ra80 minimum for most applications; Ra90+ for retail or areas where colour accuracy matters.

B22 — Bayonet Cap (BC)

The B22 bayonet cap is the traditional British lamp cap: two side pins at 180° that engage bayonet slots in the lampholder with a push-and-twist action. B22 (also written BC, for Bayonet Cap) is standard in most UK pendant fittings, table lamps, floor lamps, and older ceiling roses wired with the loop-in-loop method (see our ceiling rose guide). It also fits T2 batten holders in garages, utility rooms, and commercial premises.

The smaller B15 (SBC, Small Bayonet Cap) uses the same push-and-twist action but at 15 mm diameter and is found in nightlights, small decorative fittings, and indicator lamps. Do not confuse B22 with B15 — the fitting body makes them mechanically incompatible.

When to specify B22: pendant light replacement, table and floor lamp conversions, batten holder (BC) installations in garages and commercial spaces, and any fitting purchased in the UK before circa 2010 that did not use a screw cap. Filament-style B22 LEDs are the most popular aesthetic choice for open-shade and decorative fittings.

E27 — Large Edison Screw (ES)

The E27 Edison screw has a 27 mm diameter threaded brass or aluminium shell. It screws clockwise into the lampholder until firm — no click, unlike bayonet. E27 is used widely across Europe, North America, and Asia and is increasingly common in UK floor lamps, designer pendants, and large commercial filament-style fittings. Most E27 lampholders and GLS lamps are identical in dimensions to B22, and some pendant fittings ship with interchangeable lampholder rings accepting either cap — check the fitting before ordering.

When to specify E27: floor lamp conversions, replacement of vintage Edison-screw filament lamps in industrial-style pendants, large globe fittings, and commercial high-bay luminaires that accept E27 mogul variants. The plastic body LED (such as the Meridian 9.5W) is suitable for fully enclosed globes or lampshades where heat retention could be an issue; filament-style LEDs are better suited to open shades.

E14 — Small Edison Screw (SES)

The E14 small Edison screw has a 14 mm diameter thread and is found in small candle fittings, chandeliers, multi-arm pendant fittings, bathroom mirror strips, and decorative table lamps. The candle profile (C35 or C37) and golf-ball profile (G45) are the most common lamp shapes in E14. SBC (B15) is the bayonet equivalent and serves the same applications in older UK-origin fittings.

When to specify E14: chandelier and multi-arm fitting conversions (confirm how many lamps per circuit and total watt loading on the lampholder wiring); bathroom mirror lights (check IP rating of the fitting for zone compliance under BS 7671 Section 701); decorative table lamp conversions. A 4W E14 LED replaces a 35–40W incandescent candle: on a 12-lamp chandelier this reduces the load from 420–480W to 48W, a significant saving that may also allow the circuit to be protected by a smaller MCB.

LED Lumen Equivalence and Wattage Selection

The legacy watts-to-brightness relationship no longer applies once you move from incandescent to LED. Use lumens (the measure of light output) rather than watts to select the right replacement lamp.

Minimum lumen output for lighting design: the CIBSE and BS 8206 guidance on maintained illuminance gives typical values — 150 lux for domestic hallways, 300 lux for kitchens, 500 lux for task areas. Calculate the number of lamps needed from the room area, lamp lumen output, and utilisation factor rather than simply replacing like-for-like wattage.

Colour Temperature and Colour Rendering Index (CRI)

Colour temperature is measured in Kelvin (K). The three common bands:

• 2700K — Warm White: a yellow-white light close to incandescent. Standard for domestic living rooms, bedrooms, and hospitality. Creates a relaxed atmosphere and flatters skin tones.
• 4000K — Cool White / Natural White: a crisp, neutral white. Standard for kitchens, offices, retail, and commercial spaces. Improves task visibility over warm white.
• 6500K — Daylight: a blue-white light close to overcast daylight. Used in workshops, laboratories, art studios, and inspection areas where colour accuracy and alertness matter.

CRI (Colour Rendering Index, Ra) measures how accurately a light source renders colours relative to natural daylight (Ra 100). The legal minimum for UK commercial premises under the Building Regulations Part L is Ra 80. For retail, gallery, or medical environments specify Ra 90+ LEDs. Most budget GU10 and GLS LEDs are Ra 80; filament-style LEDs typically achieve Ra 90–95 due to the full-spectrum nature of the phosphor-coated filament.

Dimming Compatibility

Not all LED lamps are dimmable, and not all dimmable LEDs are compatible with every dimmer switch. The key matching rules:

• Non-dimmable LED + dimmer switch: the lamp will either not dim, flicker badly, buzz, or fail prematurely. Some non-dimmable LEDs will also emit heat when connected to a dimmer set below 100% output. Always use a dimmable LED on a dimmer circuit.
• Leading-edge (LE) dimmers (the older TRIAC type, often used with halogen): compatible with a narrower range of dimmable LEDs. Maximum load is typically 100–400W; minimum load may be 10–25W, which means fewer than 5–10 LED lamps on a single circuit may fall below the minimum and cause flicker. Replace LE dimmers with trailing-edge (TE) dimmer switches when switching to LED.
• Trailing-edge (TE) dimmers: compatible with most dimmable LEDs. Lower minimum load (typically 1–5W), smoother dimming curve, and no audible buzz. See our dimmer switches guide for selection guidance.
• Smart dimmer switches and wireless systems: confirm lamp compatibility with the dimmer manufacturer's approved lamp list. Lutron, Varilight, and Legrand publish compatibility tables for their smart dimming products.

Enclosed Fittings and Thermal Management

Many LED lamps carry a warning: "Not suitable for use in enclosed fittings." This matters because LED driver electronics are temperature-sensitive — an enclosed globe or downlight cover traps the heat generated by the driver, reducing lamp life and potentially causing premature failure. Always check the lamp datasheet before installing in a fully enclosed fitting.

LEDs rated for enclosed fittings include ceramic-body GU10s, some plastic-body GLS lamps (such as the Meridian 9.5W), and specialised high-temperature range lamps. Filament-style LEDs (e.g. the Integral Omni Candle E14) are typically not suitable for enclosed fittings because the warm driver electronics inside the narrow base have no airflow path.

Wiring Regulations and Part P

Replacing a lamp or lamp cap type is not notifiable work under the Building Regulations Part P — it is considered maintenance. However, if you are replacing a lampholder (e.g. from a B22 batten holder to a GU10 downlight fitting), fitting new luminaires, or extending a lighting circuit, the work is notifiable and must be carried out by a qualified electrician or registered with a Part P competent persons scheme (NICEIC, ELECSA, NAPIT).

In bathrooms, luminaire replacement in Zone 1 (above the bath or shower tray, up to 2.25 m from the floor) must be like-for-like in terms of IP rating and voltage — replacing a 12V LED downlight with a 230V GU10 is not like-for-like and is notifiable. See BS 7671 Section 701 and our bathroom electrical accessories guide for zone compliance details.

Lamp Disposal: the WEEE Directive

LED lamps contain electronic components that classify them as Waste Electrical and Electronic Equipment (WEEE) under the WEEE Regulations 2013. Do not dispose of LED lamps in general household waste. Return to a retailer collection point or local authority WEEE facility. CFL lamps contain mercury and have additional handling requirements — seal in a plastic bag before disposal and take to a household hazardous waste facility or electrical retailer.

Choosing the Right LED Lamp — Checklist

1. Identify the lamp cap type: GU10, B22, E27, E14, or another type.
2. Measure the lamp shape and size if replacing in a tight fitting — check the overall length (OAL) and maximum diameter of the replacement against the fitting dimensions.
3. Choose lumen output based on the required illuminance level, not watts.
4. Select colour temperature for the application (2700K domestic, 4000K commercial/kitchen).
5. Check CRI requirement — Ra80 minimum, Ra90+ for retail or colour-critical work.
6. If the circuit has a dimmer switch, confirm the lamp is dimmable and is listed as compatible with the dimmer type (TE preferred).
7. Check enclosed fitting compatibility if installing in a globe, globe diffuser, or fully enclosed downlight cover.
8. Verify the beam angle — GU10 spotlights are available in 25°, 36°, 60°, and 120° beam angles; select to suit whether you need a focused spot or a wide flood.

Related Guides

• LED Downlights — Fire-Rated, IP65, and Recessed Downlights
• LED Batten Lights and Fluorescent Tube Replacements
• LED Strip Lights and LED Tape
• Dimmer Switches — Leading Edge, Trailing Edge, and LED Compatibility
• Bathroom Electrical Accessories — Zone Wiring and IP Ratings
• Ceiling Roses and Batten Holders — BC Fittings and Loop-In-Loop Wiring
• PIR LED Security Floodlights
• Light Switches — 1-Way, 2-Way, and Intermediate Wiring