Lighting Design for Living Spaces: Lux, Kelvin and the Three Layers

First, an honest framing: no lighting standard exists for private residential spaces. The European standard EN 12464-1 governs the lighting of workplaces – yet its values serve residential lighting design as a proven reference, and the Swiss standard SIA 500 refers to its minimum values for residential buildings. From this, reliable guide values can be derived: around 100 lux for hallways and circulation areas, 200 lux for stairs and cloakrooms, 500 lux for reading, work and kitchen work areas. Once you know this spread, you understand the most important principle of lighting design: it is not the room that needs a brightness level – it is the activity.

Color temperature is stated in Kelvin and divided normatively into three groups: warm white below 3300 K, neutral white between 3300 and 5300 K, daylight white above. Which light color “belongs” in which room, by contrast, is convention and taste – there are no scientifically fixed feel-good values per room. What has proven itself in practice: warm white for living and sleeping areas, more neutral light where concentrated work takes place – and staying with one light color within a given zone, because mixtures feel restless.

On one point, the research is clear: light is the primary zeitgeber of the internal clock, and bright, short-wavelength (blue) light in the evening disrupts sleep. In its position statement, the International Commission on Illumination CIE explicitly recommends keeping the biologically effective (melanopic) light dose low in the evening. A randomized study in PNAS demonstrated the mechanism drastically: evening reading on a light-emitting display suppressed melatonin release by around 55 percent and shifted the internal clock by more than an hour and a half – compared with a printed book. The study concerned displays, not room lighting, and was small (12 participants); it nevertheless clearly supports the direction of the recommendation: warm light colors and reduced brightness in the evening, especially in the bedroom.

The working tool of lighting design is the three-layer concept – an established practical convention that goes back to the lighting categories of the American lighting designer Richard Kelly from the 1950s: ambient lighting provides even orientation throughout the room, task lighting brings the necessary lux to reading, dining and work areas, accent lighting stages objects, art and architecture. What matters most is that the layers can be switched and dimmed separately – only that turns a ceiling light into a lighting mood.