Introduction: light does more than help us see
Traditional lighting design has focused on providing enough illumination for people to see their surroundings. Research over the past two decades has shown that the effects of light extend well beyond vision.
The 2017 Nobel Prize in Physiology or Medicine recognized research into circadian rhythms, bringing the relationship between light and health to wider attention. Human-centric lighting reflects this growing field of study.
GKC has integrated human-centric lighting concepts into museum, school, office and high-end residential projects in Changzhou, Suzhou, Nanjing, Shanghai and Hangzhou.
1. The scientific basis of HCL
HCL draws on human photobiology. In 2002, researchers at Brown University identified intrinsically photosensitive retinal ganglion cells (ipRGCs), a third type of light-sensitive cell in the retina.
ipRGCs are particularly sensitive to light around 480 nm. In addition to the visual system, they convey light information to the suprachiasmatic nucleus (SCN) in the hypothalamus, a central part of the body’s biological clock.
The SCN helps coordinate circadian rhythms through processes involving melatonin and cortisol. The original article describes the daily pattern as follows:
2. Three dimensions of human-centric lighting
The original article refers to DIN SPEC 67600:2013-04 and describes three dimensions to consider when planning human-centric lighting:
| Dimension | Physiological relevance | Design parameter |
|---|---|---|
| Illuminance | Alertness and cognitive performance | 300–500 lx on the working plane |
| Spectral power distribution (SPD) | Melatonin suppression | α-opic quantities under CIE S 026:2018 |
| Timing | Circadian phase | 30 minutes of higher-intensity light in the morning |
3. Melanopic EDI: a quantitative measure
In 2018, the International Commission on Illumination (CIE) published CIE S 026:2018. Melanopic equivalent daylight illuminance (melanopic EDI, or m-EDI) is used to describe the melanopic component of light exposure.
The following application values are reproduced from the original Chinese article; they are its design examples rather than a statement that CIE S 026 prescribes these application targets:
| Application | m-EDI (lx) | CCT (K) | Period |
|---|---|---|---|
| Office work | 250–500 | 4000–6500 | Morning |
| Classroom learning | 250 | 4000–5000 | Daytime |
| Hospital wards | 150–250 | 3000–4000 | Daytime |
| Preparing for sleep | <10 | <2700 | Two hours before bedtime |
| Industrial tasks | ≥250 | 4000–6500 | Working hours |
4. Applications of HCL
1. Offices: dynamic lighting can adjust colour temperature and illuminance over the day—for example, 5000 K in the morning and 4000 K in the afternoon. The original article cites productivity improvements of 10–25% from optimized HCL.
2. Education: HCL systems aim to support morning alertness without excessive afternoon stimulation. The original article attributes a 35% improvement in reading speed and a 45% reduction in errors to a study in Hamburg.
3. Healthcare: circadian lighting provides appropriate daytime light exposure and reduces blue-rich light at night to support rest and sleep.
4. Senior living: reduced sensitivity to light in older adults can call for greater light exposure. The original article describes illuminance levels of around two to three times those for younger people.
5. GKC’s approach to human-centric lighting
GKC incorporates HCL considerations throughout the design process:
• Assessment: use photobiological calculation tools to establish m-EDI targets for different functional areas.
• Luminaire selection: prioritize tunable-white luminaires with a typical adjustment range of 2700–6500 K.
• Controls: configure scheduled or sensor-triggered scene changes, including daylight tracking.
• Verification: measure on site with spectrometers and illuminance meters to compare installed performance with the design intent.
The original article describes a Changzhou international school project using tunable-white LED panels and DALI controls. Its three scheduled scenes were 5000 K / 400 lx in the morning, 4000 K / 350 lx in the afternoon and 3000 K / 250 lx in the early evening, with positive feedback from teachers, students and parents.
Conclusion
Human-centric lighting broadens lighting design from a focus on vision to a wider consideration of people. It connects lighting technology with the biological role of light in daily life.
For architects, interior designers and clients, understanding HCL principles can inform more comfortable and supportive environments. GKC works with project teams to create scientifically informed, people-focused lighting.
References
Sources for the related figures and research mentioned in this article.
[1] The Nobel Prize in Physiology or Medicine 2017 — NobelPrize.org. https://www.nobelprize.org/prizes/medicine/2017/summary/ — 2017 Nobel Prize for circadian-rhythm research
[2] Berson DM, Dunn FA, Takao M. Phototransduction by retinal ganglion cells that set the circadian clock. Science 2002;295:1070–1073. https://pubmed.ncbi.nlm.nih.gov/11834835/ — 2002 discovery of ipRGCs; peak sensitivity in the blue region (~480 nm)
[3] CIE S 026/E:2018 — CIE System for Metrology of Optical Radiation for ipRGC-Influenced Responses to Light. https://cie.co.at/publications/cie-system-metrology-optical-radiation-iprgc-influenced-responses-light-0 — CIE S 026:2018 defines α-opic quantities and melanopic EDI
[4] Barkmann C, Wessolowski N, Schulte-Markwort M. Applicability and efficacy of variable light in schools. Physiology & Behavior 2012;105(3):621–627. https://pubmed.ncbi.nlm.nih.gov/22001491/ — Hamburg (UKE) classroom study: significantly faster reading and fewer attention-test errors (the paper itself does not state percentages)
[5] LightingEurope / A.T. Kearney (2013). Human Centric Lighting: Going Beyond Energy Efficiency, p.6. https://lightingeurope.org/images/publications/general/Market_Study-Human_Centric_Lighting._Final_July_2013.pdf — Citing Barkmann et al.: error rates dropped by about 45% (comparison group 17%)
[6] Deutscher Städte- und Gemeindebund (2011). Innovatives Modellprojekt „Dynamisches Licht“ an Hamburger Schulen. https://www.dstgb.de/themen/archiv/bildung/aktuelles/innovatives-modellprojekt-dynamisches-licht-an-hamburger-schulen/ — Report on the Hamburg dynamic-lighting school project: reading speed +35% (study commissioned by Philips)
[7] Turner PL, Mainster MA. Circadian photoreception: ageing and the eye’s important role in systemic health. Br J Ophthalmol 2008;92:1439–1444. https://pmc.ncbi.nlm.nih.gov/articles/PMC2582340/ — A 65-year-old needs roughly three times the illuminance of a 25-year-old for equivalent circadian stimulation