The first LED lights only produced cool light, but now they can emit all the different shades of white you need for your different activities.

When you buy an LED light you need to think not just about the amount of light it produces (expressed in lumens), but also the colour temperature. This is expressed in kelvins and provides information on the quality of the light, namely its colour and the impression it creates.

Should I choose cool, neutral or warm light?

By playing with colour temperature, you can choose the lighting that best suits your location and requirements. You wouldn't light a bedroom or living room like a shop, warehouse or garden!

Here is how you can best use colour temperatures, from the coolest to the warmest:

Does light really have a temperature?

Kelvin is actually a unit of measurement of temperature. Water freezes at 273.15 K, or 0°C. Of course the number of kelvins displayed on the box of your LED bulb does not correspond to the physical heat emitted by the lamp, but rather designates the type of white light emitted.

There are in fact many different types of white light, but they are difficult to define and compare. We are able to perceive them to differing degrees, depending on how sensitive our eyes are. There is also a personal subjective dimension at play, namely the impression that a light produces and the feelings it provokes.

To create an objective measurement of this, scientists decided to define white lights by comparing them to the colour a cool body becomes when heated to different temperatures. It first turns red, then yellow. The higher the number of kelvins, the whiter it gets.

Don't fall into the trap!

When we talk about colour temperature, a high number of kelvins does not correspond to a 'warm' white, but rather a 'cool' white. To sum things up:

• The higher the number of kelvins, the whiter the light, producing a cool impression.
• The lower the number of kelvins, the warmer the light.