Energizer 4.2W Dimmable GLS LED Bulb B22 Cool White 4000K

The Energizer 4.2W GLS LED bulb delivers 470 lumens of 4000K cool white light through a standard B22 bayonet cap fitting. Designed as a direct replacement for traditional 40W incandescent GLS bulbs, it draws just 4.2W while providing equivalent light output. The classic GLS shape gives 270-degree light distribution, making it suitable for table lamps, ceiling pendants and wall lights where general ambient illumination is needed.

Dimmable functionality allows brightness to be adjusted from full 470 lumens down to around 10% output, depending on the dimmer switch installed. This makes the bulb adaptable for kitchens and workspaces needing task lighting during the day, and living rooms or bedrooms where lower evening light levels are preferred. The 4000K colour temperature sits between warm white and daylight, giving neutral white light that renders colours accurately without the yellow cast of 2700K bulbs or the blue tint of 6500K daylight bulbs.

The B22 bayonet cap is the standard UK fitting for most domestic light fixtures manufactured before the mid-2000s. The bulb inserts with a push-and-twist motion and locks securely into the lampholder. Energy rating E reflects the efficiency standards introduced in September 2021 under EU and UK regulations, placing this bulb in the mid-range of current LED performance. Energizer rates the lifespan at 15,000 hours, equivalent to approximately 15 years of use at 3 hours per day.

Is this bulb compatible with all dimmer switches?

The bulb is rated as dimmable, but performance depends on the dimmer switch model. Older rotary dimmers designed for incandescent bulbs may cause flickering or buzzing. For best results, use a trailing-edge or LED-compatible dimmer. If uncertain about your existing dimmer, contact us before purchase.

What does 4000K cool white look like compared to warm white?

4000K gives a neutral white light without the yellow tint of 2700K-3000K warm white bulbs. It appears crisper and closer to natural daylight, making it preferred for kitchens, bathrooms and workspaces. Living rooms and bedrooms traditionally use warmer tones, but 4000K works well in modern interiors with grey or white colour schemes.

How long does the bulb last?

Energizer rates this bulb at 15,000 hours. At 3 hours of use per day, that translates to approximately 15 years before the light output degrades below 70% of the initial 470 lumens. The bulb does not fail suddenly like an incandescent filament — it gradually dims over time.

Can I use this in an enclosed fitting?

Yes. The GLS shape and low heat output of LED technology mean this bulb is safe in fully enclosed ceiling lights, table lamp shades and wall fittings. Unlike some high-wattage LEDs, the 4.2W draw does not require additional ventilation.