July 18, 2026 Shopify API

LED GLS Bulbs — BC (B22) and ES (E27), Dimmable, Filament and Standard Guide for UK Electricians

What Is a GLS Bulb?

GLS stands for General Lamp Shape — the classic A-shape bulb that replaced incandescent lighting for over a century. LED GLS bulbs replicate this profile while consuming 80–90% less energy. They fit standard pendant fittings, table lamps, floor lamps, and open ceiling roses with no rewiring required.

For UK electricians, understanding GLS specifications — cap type, wattage equivalent, lumen output, and dimmability — is essential when specifying replacement lamps for domestic and light-commercial installations.

B22 vs E27: Which Cap Do You Need?

UK installations use two primary GLS cap types:

B22 (BC — Bayonet Cap): The standard UK bayonet fitting. Push-and-twist insertion. Dominant in domestic properties, particularly older housing stock. Identified by two side pins.
E27 (ES — Edison Screw): The European standard screw fitting. More common in newer fittings, continental-style pendants, table lamps, and commercial luminaires. Clockwise thread, 27mm diameter.

Always confirm the fitting type before ordering. B22 and E27 are not interchangeable without an adaptor. The smaller E14 (small ES) and B15 (small BC) variants are separate cap sizes used in decorative fittings — GLS bulbs in these sizes are less common.

Wattage Equivalents and Lumen Output

LED GLS bulbs are rated in watts (actual consumption) but marketed against incandescent equivalents. Use this guide when advising customers:

Incandescent Equivalent	Lumen Output	Typical LED Wattage
40W	~470 lm	5–6W
60W	~806 lm	7–9W
75W	~1,055 lm	8–10W
100W	~1,521 lm	12–15W
150W	~2,000 lm	14–16W

For domestic living rooms and bedrooms, a 60W equivalent (806 lm) is typical. Kitchen and utility areas often benefit from 100W equivalents (1,521 lm) for task lighting. Note that lumen output varies between manufacturers — always check the product datasheet.

Dimmable vs Non-Dimmable LED GLS

Not all LED GLS bulbs are dimmable. Key points for installations:

Non-dimmable: Standard operation on/off switching only. Lower cost. Flickering or buzzing may occur if connected to a dimmer circuit — avoid unless the circuit is non-dimmed.
Dimmable: Compatible with leading-edge (TRIAC) and trailing-edge dimmers, subject to compatibility testing. Always verify the bulb's dimmer compatibility list before installation.
Dimmer compatibility: Common UK-compatible dimmers include MK, Varilight, Lutron Caséta, and Click. LED dimmers typically require a minimum load — check the dimmer module specification when driving only one or two lamps.
Part P compliance: Replacing lamp types in a dwelling is a minor work item under Part P. No notification required when the luminaire and wiring are unchanged.

Filament LED GLS vs Standard LED GLS

Two LED technologies dominate the GLS market:

Standard (frosted) LED GLS: Light diffused through a frosted globe. Even illumination, no visible hotspot. Best for pendant fittings, shaded lamps, and applications where the bulb is not directly visible.
Filament LED GLS: Visible LED filament strips in a clear glass envelope. Replicates the aesthetic of classic Edison incandescent bulbs. Typically 2200K–2700K warm white. Popular in exposed-bulb pendants, decorative fittings, and heritage-style installations. Usually dimmable. Slightly lower efficacy than standard frosted LED at equivalent wattage.

Filament GLS bulbs are not recommended for enclosed fittings — heat build-up reduces LED life significantly. Standard frosted GLS may also have enclosed-fitting restrictions — check the IP rating and thermal specification on the datasheet.

Colour Temperature Guide

LED GLS bulbs are available across the full colour temperature range:

2700K (Warm White): Closest to incandescent light. Preferred for living rooms, bedrooms, and hospitality environments. Relaxing, amber tone.
3000K (Warm White/Neutral): Slightly crisper than 2700K. Common in retail and kitchen environments.
4000K (Cool White): Neutral daylight. Suitable for kitchens, bathrooms, offices. Improves visibility for task work.
5000K+ (Daylight): Bluish-white light. Used in commercial, industrial, and specialist applications. Less common in domestic GLS.

Energy Efficiency and Lamp Life

LED GLS bulbs typically achieve:

Rated life: 15,000–25,000 hours (versus 1,000 hours for incandescent, 8,000 hours for CFL)
Efficacy: 80–110 lm/W (versus 10–14 lm/W for incandescent)
Energy class: Most modern LED GLS lamps achieve EU Energy Label class E or D under current 2021 regulations (replacing the old A+ system)

Replacing a single 60W incandescent with a 7W LED GLS at 8 hours/day use saves approximately 38 kWh per year — around £9.50 at current UK electricity rates. For properties with 20+ lamp positions, whole-house LED conversion offers significant operating cost reductions.

Installation Notes

Ensure supply is isolated before replacing lamps in B22 or E27 holders
Do not exceed the maximum wattage rating marked on the luminaire — LED wattage is actual consumption, not incandescent equivalent
For enclosed fittings, check the LED lamp's enclosed-fitting suitability (often marked with a flame symbol)
Dimmable circuits: confirm dimmer module minimum load is not exceeded with LED lamps — ghost switching or flicker indicates incompatibility
B22 bayonet holders deteriorate over time — if the lamp is loose or intermittent, inspect and replace the lampholder (MK, Crabtree and Click holders are stocked at APM)