Circadian Light Meter
Patient-centric circadian lighting for Indian healthcare environments. Pick a time of day and intensity, and the tool computes CCT, melanopic lux (EML / mEDI), melatonin suppression, and the relative alertness curve. Calibrated against WELL v2 L03, CIE S 026:2018, and the action-spectrum literature (Brainard 2001, Lucas et al. 2014).
Circadian Wellness Lab
Biological goal: Inhibiting Melatonin for Alertness
CCT
6500 K
EML
550
Suppression
97%
↑ Relative Alertness (%)
Time (h) →
WELL v2 L03 daytime ✓
EML ≥ 200 (08:00–18:00)
Sleep / night —
EML < 50 (21:00–07:00)
Phase-appropriate ✓
EML matches biological phase
Methodology & standards
| Source | Application | Threshold | Notes |
|---|---|---|---|
| WELL v2 L03 | Circadian Lighting Design | EML ≥ 200 | Daytime patient/work areas; minimum 4 hours/day. |
| CIE S 026:2018 | Melanopic light measurement | mEDI | Replaces legacy EML; uses melanopic action spectrum. |
| DIN SPEC 67600 | Biologically effective lighting | CCT × Lux | German standard with hourly target curve. |
| NABH 5th Edition | Indian hospital accreditation | — | No numeric circadian standard — gap. Architects should specify against WELL v2. |
| ECBC 2017 | Indian energy code (lighting) | LPD | Lighting power density only — silent on CCT/EML. |
EML formula
EML = lux × melanopic-ratio(CCT)
Melanopic ratio is the EML/lux conversion factor, weighted by the melanopic action spectrum (peak ~480 nm). Values: 2700 K ≈ 0.45, 4000 K ≈ 0.65, 6500 K ≈ 1.10.
Suppression curve
S = 1 − exp(−EML / 150)
Saturating Hill-style curve. Calibrated against Brainard 2001, Thapan 2001, Lucas et al. 2014: EML 100 → ~50%, EML 300 → ~85%, EML 500 → ~96%.
Alertness curve
Approximation of the Borbély two-process model: morning rise (06:00–10:00), post-lunch dip (~16:00–18:00), evening second wind (~21:00). Hourly anchors, linear interpolation. Use as a phase guide, not a clinical predictor.
References (Harvard)
- International WELL Building Institute (2020) WELL v2: Light, Concept L03 — Circadian Lighting Design. New York: IWBI.
- Commission Internationale de l’Éclairage (2018) CIE S 026/E:2018 System for Metrology of Optical Radiation for ipRGC- Influenced Responses to Light. Vienna: CIE.
- Brainard, G.C., Hanifin, J.P., Greeson, J.M., Byrne, B., Glickman, G., Gerner, E. & Rollag, M.D. (2001) ‘Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor’, Journal of Neuroscience, 21(16), pp. 6405–6412.
- Thapan, K., Arendt, J. & Skene, D.J. (2001) ‘An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans’, Journal of Physiology, 535(1), pp. 261–267.
- Lucas, R.J. et al. (2014) ‘Measuring and using light in the melanopsin age’, Trends in Neurosciences, 37(1), pp. 1–9.
- Borbély, A.A. (1982) ‘A two process model of sleep regulation’, Human Neurobiology, 1(3), pp. 195–204.
- DIN (2013) DIN SPEC 67600: Biologically Effective Illumination — Design Guidelines. Berlin: Deutsches Institut für Normung.
- NABH (2020) Standards for Hospitals, 5th Edition. New Delhi: Quality Council of India.
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