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What is colour temperature and how do you choose Kelvin?
Lighting
Colour temperature in Kelvin decides whether light feels warm or cool. How to choose 2700K, 3000K or 4000K for offices, retail and homes.
What colour temperature is
Colour temperature describes the tint of white light: warmer (yellowish) or cooler (bluish). It is expressed in kelvin (K). It does not tell you how much light there is (that is flux or lux), but the colour of that light.
With LED, the wrong kelvin changes the atmosphere of a space even when illuminance is correct. The same office at 2700 K feels residential; at 4000 K it feels like a workplace.
The kelvin scale: from 2200 K to 6500 K
Typical interior values:
- 2200–2700 K: extra-warm white. Hospitality, residential, relaxation.
- 3000 K: warm white. Retail, hotels, comfort-led offices.
- 3500–4000 K: neutral white. Offices, classrooms, clinics, light industry.
- 5000–6500 K: cool white or daylight. High-concentration tasks, inspection or outdoors. All-day interiors can feel harsh.
Marketing labels (warm white, cool white) do not replace the kelvin value on the datasheet.
How to choose kelvin by space
- Offices and classrooms: 4000 K is the productivity standard; 3000 K if you want a less clinical feel.
- Retail and supermarket: 3000–4000 K depending on brand; bakery and produce often need warmer tones.
- Hotels and homes: 2700–3000 K in rooms; neutral in back of house.
- Museums: 3000–3500 K often balances conservation and colour fidelity.
- Hospitals and care homes: neutral in clinical areas; warmer in living and rest spaces.
If the project includes tunable white (CCT), kelvin can change through the day without swapping luminaires.
Colour temperature, CRI and dimming
Kelvin does not guarantee faithful colours. You still need a high CRI (and high R9 in retail or art). 4000 K at CRI 80 does not look like 4000 K at CRI 90.
When dimming fixed-CCT LEDs, some ranges lose spectral quality at low levels. Specify drivers and modules designed for deep dimming.
Common mistakes when choosing kelvin
- Mixing 3000 K and 4000 K in the same visual field without design intent.
- Using 6500 K in offices all day.
- Choosing from a generic catalogue without samples on real materials (wood, stone, textile).
- Forgetting that paint, flooring and daylight shift how white is perceived.
Frequently asked questions
What colour temperature is best for work?
In most offices, 4000 K with good UGR and CRI ≥80 (ideally ≥90). With human centric lighting, start warmer in the morning and move to neutral in core hours.
2700 K or 3000 K at home and in hotels?
2700 K is more intimate; 3000 K is warm but clearer for common areas. Both work with high CRI and no glare.
Can kelvin be changed later?
Not with fixed-CCT luminaires. With tunable white or a control system (DALI-2 DT8, Casambi, etc.), yes, within the product range.
How Celux can help
As a lighting manufacturer we specify kelvin, CRI and optics together. If you are choosing colour temperature for a project, we can review samples and specify consistent luminaires across the building.
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