GU10 LED Bulb 4.2W 345lm Non-Dimmable - Cool White 4000K, 4 Pack

This GU10 spotlight draws 4.2W and gives 345 lumens of 4,000K cool white light. GU10 is the twist and lock cap with two stubby pins on the base, the standard mains voltage fitting used in ceiling downlights and track spots, so there is no transformer or driver involved and the lamp goes straight onto the existing lampholder. The pack rates it as a 50W replacement. Light leaves the front lens in a 36 degree cone, which is what a reflector lamp is chosen for: a defined pool of light rather than a general wash across the ceiling.

Cool white at 4,000K sits between the yellow cast of a 2,700K lamp and the blue of a daylight bulb. It reads as a clean neutral white and holds edges and detail well, which is why it suits kitchens, utility rooms, garages, workshops, home offices and display shelving, anywhere you are looking closely at something rather than settling in for the evening. One thing worth planning before you buy: colour temperatures mix badly, so if a room already runs on warm white lamps, changing only two or three will read as a patch of different light. Do a whole circuit at a time. With a 36 degree beam, spacing the fittings at roughly the ceiling height gives overlapping pools rather than hard scallops down a wall.

The pack marks these as non dimmable. They want a plain on and off switch; left on an old rotary dimmer meant for halogen, a non dimming LED can flicker, buzz or fail early, so change the dimmer for a switch or choose a dimmable lamp instead. The energy label reads class F at 5kWh per 1,000 hours, and the pack prints a 15 year lifespan. The rating is IP20, so these are for dry indoor positions. One unit is a box of four lamps.

Will these fit my existing halogen downlights?

If the old lamp has a GU10 cap, two stubby pins that twist and lock into the holder, yes. GU10 runs on mains voltage, so there is no transformer to check or remove first.

How many bulbs do I actually receive?

One unit is a sealed box of four lamps. The minimum order on this listing is 21 units, sold in multiples of 21, so the smallest purchase is 21 boxes.

Can I put these on a dimmer switch?

No. The pack marks them non dimmable, so they need a plain on and off switch. On an existing halogen dimmer they may flicker, hum or have a shortened life.

How bright will they be next to my old halogens?

Each lamp puts out 345 lumens and the pack rates it as a 50W replacement, with the output concentrated into a 36 degree cone rather than spread evenly across the room.

What does 4,000K cool white actually look like?

A clean neutral white with no yellow in it, brighter feeling than a 2,700K warm white lamp and softer than a 6,500K daylight one. Good over worktops and workbenches.

How far apart should I space the fittings?

With a 36 degree beam, spacing roughly equal to the ceiling height gives pools of light that overlap at worktop level, which avoids dark gaps between the spots.