Warm or cool light: understanding kelvins

We often choose a bulb for its wattage or its shape. Yet the number that matters most for atmosphere lies elsewhere: the colour temperature, expressed in kelvins (K). It tells you whether the light will be warm like a flame or white like a midday sky.

What kelvins measure

The lower the number, the warmer the light, that is, the more orange. The higher it is, the whiter the light becomes, then bluish. A candle is around 1800 K, an old incandescent bulb about 2700 K, daylight in the middle of the day between 5000 and 6500 K.

The benchmarks to remember

• 2700 K, very warm white: the light of evenings, close to the old incandescent bulb. For the living room and the bedroom.
• 3000 K, warm white: a little sharper, still soft. For the bedside, the dining room, the entrance hall.
• 3500 K, lighter warm white: crisp without being cold. For a dinner table, a console, a kitchen.
• 4000 K, neutral white: the light for work. For a study, a bathroom, a dressing room.
• 5000 K and above, cool white: best kept for garages and utility rooms.

The same warmth throughout a room

The greatest flaw in lighting is not being too warm or too cool: it is mixing the two. A 2700 K floor lamp next to a 4000 K ceiling light, and the room looks out of tune. In the evening, keep your lights close to one another, within a few hundred kelvins.

In the evening, a successful room is one where all the lights share the same warmth.

The case of light paintings

A light painting follows a different logic. Its LEDs emit a neutral white, at 4000 K, but this light passes through the gradient that colours it: it is the shade of the piece that gives the light its colour, on the face as on the wall. Levant diffuses an amber glow, Crépuscule a pinkish light, Heure dorée a golden light, Zénith a creamy brightness.

That is why they naturally go with warm lamps: ours range from 2700 K for Horizon and Ponant to 3000 K for the floor lamp Solstice and for Équinoxe.

What about wattage?

With LEDs, watts no longer say much about the light: they measure consumption. To know whether a lamp gives a lot of light, look at the lumens. An ambient lamp often gives a few hundred, a ceiling-light bulb 800 or more.