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About this tool
Pick the right light colour temperature, CRI and lumen output for each room and mood, with a live colour preview.
This selector recommends a light colour temperature in kelvin, a minimum CRI and an illuminance target for each room, then converts that target into the lamp lumens and wattage a room your size actually needs. Colour temperature follows the conventional bands — 2200–3000 K where people relax, 4000–5000 K where they work — shifted by the mood you choose, while light levels follow EN 12464-1 and the equivalent IES figures, such as 500 lux for writing and typing and 300 lux for general kitchen work. Lumens come from lux × area ÷ (utilisation factor × maintenance factor), so light that never reaches the working plane is accounted for.
Open Room Color Temperature Selector on AltFTool — it loads instantly in your browser.
Add your input to the workspace.
Adjust the options until the result looks right.
Copy or download the output and put it to work.
Colour temperature only works at the right light level, so both are recommended from the same room profile.
Utilisation and maintenance factors are applied, not just lux × area, so the fitting count is realistic.
Every temperature is shown as a swatch derived from the Planckian locus, so warm and cool are visible rather than abstract.
2700 K to 3000 K — warm white — which matches the incandescent light people associate with relaxing at home. Anything above about 4000 K reads as clinical in a room lit to 100–300 lux, which is the usual domestic ambient level.
3000 K to 4000 K works best: warm enough not to feel like an office, neutral enough to see food and knife work clearly. Aim for around 300 lux of general light and 500 lux on the worktop, with CRI 85 or better so ingredients look their real colour.
It depends on the lux target: at 300 lux with a 0.6 utilisation factor and 0.8 maintenance factor you need about 625 lamp lumens per square metre, and at 100 lux about 208. Multiply by the floor area, then divide by the output of one fitting to get the number of lamps.
It is the observation that warm light looks pleasant when it is dim while cool light only looks natural when it is bright, so a 5000 K lamp dimmed to a low level reads as gloomy and a 2200 K lamp at high output reads as oppressively yellow. Match the colour temperature to the light level you actually plan to run, and use warm-dim lamps if you dim a room deeply in the evening.