Key Takeaway
An international expert consensus recommends bright (>250 melanopic lux) daytime light, dim (<10 melanopic lux) evening light, and near-total darkness (<1 lux) during sleep to support circadian health and sleep quality.
Summary
This expert consensus statement, authored by an international panel of leading circadian and sleep researchers, provides the first evidence-based recommendations for indoor light exposure across the 24-hour day. The recommendations are grounded in decades of research on how light affects circadian rhythms, melatonin secretion, alertness, and sleep.
The panel recommends three tiers of light exposure. During the daytime, indoor light should be bright — at least 250 melanopic equivalent daylight illuminance (melanopic EDI) — to properly entrain the circadian clock and support alertness. During the evening (3 hours before sleep), light should be dimmed to below 10 melanopic EDI to avoid suppressing melatonin and delaying sleep onset. During sleep, the environment should be as dark as possible, ideally below 1 lux, to prevent disruption of sleep architecture and circadian signaling.
The recommendations use melanopic EDI as the metric rather than traditional lux, because melanopic sensitivity better reflects how light affects the circadian system through intrinsically photosensitive retinal ganglion cells (ipRGCs). The panel notes that most modern indoor environments are too dim during the day and too bright during the evening, creating a "circadian mismatch."
These guidelines have practical implications for home, workplace, and clinical lighting design. The consensus highlights that optimizing light exposure across the full day — not just avoiding blue light at night — is essential for supporting sleep, circadian alignment, and overall health.
Methods
- International expert consensus process involving researchers from circadian biology, sleep science, and lighting engineering
- Systematic review of published literature on light exposure and circadian/sleep outcomes
- Focus on melanopic equivalent daylight illuminance (melanopic EDI) as the primary metric
- Recommendations stratified by time of day: daytime, evening (3 hours pre-sleep), and nighttime (during sleep)
- Published in PLoS Biology as an open-access consensus statement
Key Results
- Daytime recommendation: Indoor light should be ≥250 melanopic EDI (equivalent to bright indoor or daylight-supplemented lighting)
- Evening recommendation: Light should be ≤10 melanopic EDI in the 3 hours before bed (equivalent to dim, warm-toned lighting)
- Nighttime recommendation: Light during sleep should be as low as possible, ideally <1 lux
- Most modern indoor environments fall well below daytime recommendations (~50-100 lux typical office)
- Evening home environments commonly exceed the 10 melanopic EDI threshold
- Blue-enriched light in the evening is especially disruptive, but intensity matters more than spectrum alone
- Practical guidance: use warm-toned, dimmable lighting in evenings; maximize daylight exposure during the day
Limitations
- Consensus statement, not a primary research study — recommendations are based on existing evidence, not new experiments
- Individual sensitivity to light varies (age, chronotype, prior light history)
- Melanopic EDI is not yet widely adopted or easily measured by consumers
- Recommendations may be difficult to implement in all built environments (older buildings, certain climates)
- Limited evidence base for precise thresholds — many values are best estimates
- Does not address shift workers or individuals with circadian disorders in detail