Energizer 4.2W Dimmable GLS LED Bulb E27 4000K Cool White

The Energizer 4.2W GLS LED bulb delivers 470 lumens of 4000K cool white light through a standard E27 Edison screw base. The bulb replaces a traditional 40W incandescent while drawing just 4.2W on 230V mains, giving the same light output at approximately 10% of the running cost. The GLS (General Lighting Service) shape matches the classic bulb form that fits most table lamps, ceiling pendants and standard light fittings without adaptor rings.

Designed for rooms where bright, neutral-toned light supports activity and concentration, the 4000K colour temperature sits between warm white and daylight. This makes it suitable for kitchens, home offices, bathrooms and utility rooms where task visibility matters more than ambient warmth. The bulb is fully dimmable when paired with a compatible LED dimmer switch, allowing output to be reduced from full 470-lumen brightness down to a lower evening level without flicker.

The bulb carries an E energy rating under the 2021 EU energy label regulations and is rated for 15,000 hours of operation, which translates to approximately 13 years at 3 hours daily use. The frosted glass envelope diffuses the LED array inside, preventing visible point sources and giving an even light distribution across the room. The cool white tone renders colours more neutrally than warm white, making it easier to distinguish detail in printed materials, food preparation and precision tasks.

Is this bulb compatible with standard dimmer switches?

Yes, the Energizer 4.2W GLS is rated as dimmable. It works with most LED-compatible dimmer switches, but older dimmer models designed only for incandescent bulbs may cause flicker or limited dimming range. If your existing dimmer is more than 10 years old, you may need to upgrade to an LED-rated dimmer for smooth operation.

What's the difference between 4000K and warm white bulbs?

4000K cool white gives a neutral, slightly blue-toned light that resembles midday overcast sky. Warm white bulbs (2700K-3000K) give a yellower, cosier tone similar to traditional incandescent bulbs. Cool white is preferred for task-focused spaces like kitchens and offices, while warm white suits living rooms and bedrooms where relaxation is the priority.

How much does it cost to run compared to a 40W incandescent?

At UK average electricity rates of approximately 24p per kWh, a 40W incandescent bulb costs around 1p per hour to run. This 4.2W LED costs approximately 0.1p per hour, giving a 90% reduction in running cost for the same light output.

Will it fit my existing lamp shade or fixture?

The GLS shape is the standard bulb profile used in most household table lamps, ceiling pendants and wall lights designed for E27 Edison screw bulbs. The bulb diameter is approximately 60mm and the overall length is approximately 110mm, which matches traditional incandescent GLS dimensions.