Warm white vs cool white: which light colour for which room

In short. Warm white (2700K to 3000K) is the yellow-white of an old incandescent globe and suits living rooms, bedrooms, dining and hallways. Cool white (4000K) is a neutral white for kitchens, bathrooms, laundries, garages and offices. Daylight (5000K and above) is blue-white and belongs in workshops and retail, not in homes. The Kelvin number is printed on every globe and downlight box, and every light in one room should carry the same number.

Approximate screen rendering of each colour temperature; the showroom has them lit side by side.

What do the Kelvin numbers mean?

Colour temperature is measured in Kelvin. Lower numbers are warmer and more orange, higher numbers are cooler and bluer, which is the opposite of how the words sound. 2700K matches a traditional incandescent globe; 3000K is a touch whiter and is the most common warm white in LED fittings; 4000K is the white of a modern office; 5000K to 6500K approaches overcast daylight.

Which colour for which room?

• Living room, bedrooms, dining, hallway: 2700K or 3000K. Skin tones, timber and warm paint colours look right, and the room reads as relaxed in the evening.
• Kitchen bench and bathroom mirror: 4000K for the task light, so food and faces show true colour. The general light in the same room can stay warm.
• Laundry, garage, study: 4000K. Cooler light helps concentration and shows dirt.
• Outdoors: 3000K. Cool white on a house front looks like a car park, and warm light is kinder to neighbours and to insects.

How do I match new globes to old ones?

Read the box of an existing globe, or bring one in. If you are replacing halogen downlights with LED and the room felt right before, choose 3000K; halogen sits at about 2800K and most people find 2700K LED slightly too orange beside it. Where the paint and furniture are not chosen yet, tri-colour LED downlights with a 3000K, 4000K and 5000K switch let the electrician set the colour on the day and change it later.

Does colour temperature change the brightness?

No. Brightness is lumens, colour is Kelvin, and they are printed separately. A 4000K globe looks brighter than a 3000K globe of the same lumens because the eye reads cooler light as crisper, which is why a cool-white living room can feel harsh at night even at a low setting.

Where this fits at Cosmo

• Light globes at Cosmo
• LED downlights & ceiling lights at Cosmo
• LED strip & smart lighting at Cosmo