By Anne McKenna, KES Lighting & Home. Last updated 14 September 2026.
Warm white, 2700K, for every room you sit in. 3000K where you work with your hands, so over a kitchen worktop or at a bathroom mirror. 4000K, which is what 'cool white' usually means, only in a utility room, a garage or a home office by day. That is the whole answer, and if you buy to that rule the house will look right at night. Nearly every house that looks wrong after dark has broken it, usually by accident.
The number that does all this is printed on the side of every bulb box and almost nobody reads it. It is measured in Kelvin, written as K, and it decides whether a room feels like a home or a waiting room. It costs nothing to get right and it costs a bulb to fix. Here is the scale, then the answer room by room, then the questions we get asked most.
The Kelvin scale, and what the words on the box mean
Low numbers are warm and golden. High numbers are cool and blue. The words on the packet ('warm white', 'cool white', 'daylight') are not standardised, so two boxes marked 'warm white' can be different colours. The number is the only thing to trust.
| Kelvin | What it looks like | Where it belongs |
|---|---|---|
| 2200K and below | Candle glow, amber | Filament lamps on show, the last hour of the evening, dimmed low |
| 2700K | Warm white, the colour of the old incandescent bulb | Living room, dining room, bedroom, hallway, snug. The default |
| 3000K | Warm white, a touch whiter and crisper | Kitchen worktop, bathroom, a reading corner, outside |
| 4000K | Cool white, sometimes sold as natural white. No golden cast at all | Utility room, garage, workshop, home office in the daytime |
| 5000K and above | Daylight, blue-white | Not in a home. Commercial and industrial light |
Two things people get wrong about the scale. First, 3000K is not 'cool'. It is still warm white, just a little less golden than 2700K, and the two sit together happily in the same house. Second, the jump from 3000K to 4000K is the one you notice. That is the line between a home and an office, and it is the line most accidental purchases cross.
Living room: 2700K, and nothing cooler
This is the room you sit in with the lights on for longest, so it is the room where the number matters most. 2700K, throughout, on every lamp and on the ceiling. It flatters paint colours, it flatters people, and it reads as evening. We would not put 3000K in a living room unless the whole scheme was very pale and modern, and we would never put 4000K in one.
If your living room feels cold and you cannot say why, check every bulb in it. The usual culprit is one 4000K lamp somebody bought in a hurry, sitting next to two 2700K ones. The room never settles because the light does not agree with itself. Match them and the room changes that evening. Our guide to layering a room covers where the lamps go once the colour is right.
Kitchen: 3000K over the worktop, 2700K over the table
The kitchen is the one room where we will argue for two temperatures, because it does two jobs. Over the worktop, where you are chopping and reading a recipe, 3000K is the right call: crisp enough to see by, still warm enough that the room belongs to the house. Over the table, or on the pendants over an island where people sit, 2700K, because that half of the room is a dining room by seven o'clock.
Is 3000K or 4000K better for a kitchen? 3000K, and it is not close. 4000K downlights across a kitchen ceiling are the single commonest reason a new kitchen looks like a showroom instead of a home, and the people who fitted them usually did it because 'kitchen' and 'bright' got muddled with 'cool'. Brightness is lumens, not Kelvin. You can have a bright, warm kitchen. If you have already got 4000K in the ceiling and hate it, the fix is a box of GU10 lamps in 3000K, and an afternoon.
Bedroom: 2700K, on a dimmer
2700K, with everything on a dimmer if you can manage it, and the cooler lamps kept out altogether. Warm, low light in the evening is the signal the body reads as bedtime, and a 4000K ceiling light in a bedroom works against you every night. The one exception is a dressing table or a make-up mirror, which can go a little cooler on its own switch. We wrote the bedroom up on its own, with the reasoning: what colour temperature is best for a bedroom.
Bathroom: 3000K, and light at the mirror from the sides
3000K suits a bathroom. It is clean without being cold, and it keeps white tiles looking white rather than yellow. Go to 4000K at the mirror only if you do close work there and want it more like daylight, and keep that on a separate switch from the ceiling. What matters more than the number in a bathroom is where the light comes from: straight overhead drops shadow into your eyes, from the sides at face height does not. See bathroom mirror and vanity lighting, and check the zone rating on anything you buy for this room.
Hallway, landing and stairs: 2700K, the same as the rooms off them
A hall is the join between every other room, so give it the same temperature as the rooms it leads to, which in most houses means 2700K. A cool white hall between two warm rooms reads as a corridor, and it is the first thing a visitor sees. If the stairs need more light for safety, add fittings or lumens, not Kelvin.
Home office and utility: 4000K by day, 2700K if you work at night
This is where cool white earns its keep. 4000K at a desk in daylight hours keeps you alert and shows a document as it is. A utility room, garage or workshop can take 4000K without apology, because nobody is relaxing in there. The catch is the evening: if the office is also where you sit at nine at night, a 4000K ceiling light will keep you wired. Either put a 2700K lamp on the desk for after dark, or accept that the room has one job.
Outside: 2700K to 3000K, never daylight
Warm on the house, always. A 2700K or 3000K lantern by the front door reads as welcome. A 5000K or 6000K floodlight reads as a car park, and it makes the brickwork look grey. Security lights are the usual offender; if yours is blue-white, the sensor is fine and the lamp is wrong.
Can you mix warm white and cool white?
Between rooms, yes, and the kitchen above is the worked example. Within one room, no. One Kelvin number per room is the rule that fixes more houses than any other, and it is the one we would overrule you on. Two 2700K lamps and one 3000K in the same room is a mild mismatch you will feel without naming; a 4000K lamp among 2700K ones is a mistake you will see from the doorway. When you replace one bulb, replace it with the same number, and when you cannot remember what the others are, take one out and read the side of it.
Is cool white brighter than warm white?
It looks brighter, and it is not. Brightness is lumens, and a 500 lumen lamp gives 500 lumens whether it is 2700K or 4000K. Cool white contains more blue, which the eye reads as sharper, so people reach for it when what they actually wanted was more light. Buy more lumens instead and keep the colour warm. Our guide to dimming LEDs covers the other half of that, which is turning it down again.
Which is better for your eyes, warm white or cool white?
For an evening at home, warm. Cool, blue-rich light is the daytime signal, and it is fine at a desk at eleven in the morning, but it is the wrong thing to sit under at ten at night, when it holds off the wind-down for sleep. That is the practical reason 2700K belongs in the rooms you relax in and 4000K belongs in the rooms you work in, and it is why the 'daylight' bulb that sounded cheerful on the packet ends up in the bin.
What to buy, in one paragraph
Walk round the house and read the side of one bulb in each room. Anything you sit in gets 2700K. Worktops, the bathroom and outside get 3000K. The utility room and the desk get 4000K. Buy the same number for every lamp in a room, buy dimmable where the switch allows it, and match the cap to the fitting, which is the other thing on the box. E14 or E27 is the usual question there. The full bulb range is sorted by cap, and every page carries the Kelvin number, the lumens and whether it dims.
Frequently asked questions
Which is better, warm white or cool white?
Neither is better everywhere. Warm white (2700K to 3000K) is right for every room you relax in: living room, bedroom, dining room, hallway. Cool white (4000K) is right where you work: utility room, garage, a home office by day. Most homes want warm white in nearly every room.
Is cool white brighter than warm white?
No. Brightness is measured in lumens and is the same at any colour temperature. Cool white contains more blue, which the eye reads as sharper, so it looks brighter at the same lumens. If a room needs more light, buy more lumens and keep the colour warm.
Which light is better for your eyes, warm white or cool white?
For evenings at home, warm white. Cool, blue-rich light is a daytime signal and is fine at a desk during the day, but sitting under it late at night works against winding down for sleep. Use warm white in rooms you relax in and cool white only where you work.
Is 3000K or 4000K better for a kitchen?
3000K. It is crisp enough to work under and still warm enough to feel like part of the house. 4000K across a kitchen ceiling is the commonest reason a new kitchen looks like a showroom. Use 2700K over the table or the island seating.
Should I use cool white or daylight bulbs in a kitchen?
Neither. Daylight (5000K and above) is commercial light and looks harsh in a home. Cool white (4000K) is acceptable in a utility room but too cold for most kitchens. Use 3000K over the worktop and 2700K where people sit.
Can you mix warm white and cool white in the same room?
Not in the same room. Keep one Kelvin number per room; mixing 2700K and 4000K in one space is visible from the doorway and is the usual reason a room looks wrong at night. You can use different temperatures in different rooms, for example 3000K in the kitchen and 2700K in the living room.
