Fundamentals · 20 August 2026 · 2 min read
Human-centric lighting: what the science supports
Light affects alertness and sleep, not just vision. Here is what the research supports, and how it translates into practical design decisions.
Beyond letting us see, light reaching the eye influences our body clock through specialised cells most sensitive to blue-green light. This is the basis of human-centric, or circadian, lighting — designing light that supports alertness by day and rest by night.
Measuring the effect
The international standard CIE S 026 defines melanopic equivalent daylight illuminance (melanopic EDI), a measure of light's biological effect at the eye. Expert recommendations published in 2022 suggest at least 250 lux melanopic EDI at eye level during the day, no more than 10 lux in the evening, and no more than 1 lux during sleep.
Practical design moves
- Maximise daylight first — it is the most powerful and efficient circadian light source.
- Provide bright, cooler light in daytime workspaces, with vertical light reaching the eye, not just the desk.
- Shift to warm, dim light in the evening, especially in homes and hotel rooms; warm-dim luminaires do this automatically.
- Automate the change with controls so the right light arrives without anyone thinking about it.
Building standards such as WELL now include circadian lighting criteria — a sign that how light makes us feel is becoming as important as how much of it there is.
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