Over the past 20 years, the three things we were most often asked for in projects were:
- Make the lighting look good, give the space “character”;
- Ensure illuminance meets standards, with correct Eh values;
- Achieve energy efficiency, with attractive energy reports.
Many designers have mastered this “Look + Eh + Energy” combination—but Human Centric Lighting (HCL) is quietly changing the rules.
Clients are now asking: “Does this lighting support sleep, mood, focus, or vision?”
For professional lighting designers, this is both a challenge and an opportunity for career advancement.
1. The Ceiling of Old Rules: Eh and Renderings Are No Longer Enough
Traditionally, a “well-executed lighting design” meant:
- Illuminance calculation: Horizontal illuminance (Eh) on work surfaces meets 300 / 500 / 1000 lx;
- Glare control: UGR within allowed limits;
- Energy control: Power density (W/m²) meets green building or energy standards;
- Renderings: Layered, with contrast, visually shareable.
These remain important, but HCL reminds us: people are not just a point on a lux map—they are a physiological and psychological system.
Typical blind spots:
- Indoor daytime: Eh is sufficient, but vertical eye illuminance (Ev) is too low—people can see, yet feel sleepy;
- Nighttime hotels/high-end residences: high illuminance + color temperature for “luxury” may disrupt sleep;
- Offices: beautiful renderings, but long-term work forces eyes to constantly switch between bright and dark areas;
- Schools/healthcare: designing by “classroom standards” ignores circadian rhythm and emotional recovery.
The challenge: Traditional tools and workflows are designed for “visibility + standards,” not for “how light affects people.”
2. HCL Requires Designers to Do More: From Eh to Ev, From Illuminance to Rhythm
Key terms:
- Eh (Horizontal Illuminance): Lux on horizontal surfaces, e.g., desks, floors.
- Ev (Vertical Eye Illuminance): Lux on the vertical plane at eye level, closer to the light dose the brain actually receives.
- HCL (Human Centric Lighting): Lighting designed around human physiology, cognition, emotion, and health—not just aesthetics or objects.
A conversation on HCL:
Former IALD President Jeffrey Miller once asked:
“You speak of HCL—how is it different from a lifetime of lighting design ‘for humans’?”
At first, I could only vaguely explain it in terms of rhythm, emotion, and health research.
After years of on-site measurements and practice, I now answer:
“You’ve always designed for humans. HCL asks us to go further—not just how bright a space is, but how much light the human eye actually receives (Ev).
When Eh meets task needs and Ev supports rhythm and emotion, that’s truly HCL.”
簡而言之：
- Previously: focus on space, form, style.
- Now: Eh supports tasks; Ev supports brain and body.
Practical HCL Guidelines
- From Eh to Eh + Ev
- Eh determines if a task is visible.
- Ev determines how much light the brain receives.
- Without Ev consideration: desks may be bright, but people’s brains stay in “evening mode.”
Implementation:
- In hotel rooms, offices, clinics, classrooms: evaluate Ev along typical sightlines.
- Use software + on-site measurements to manage both Eh and Ev.
- Introduce m-EDI / melanopic concepts
- Different spectra have different circadian impacts.
- 300 lx at 4000K is not equal to 300 lx at 2700K in terms of rhythm.
- Designers should answer:
- Is there enough circadian stimulus during the day?
- Is it reduced at night?
- Does tunable lighting follow this logic?
- Consider S/P Ratio
- Useful in outdoor or low-illuminance scenarios:
- Pedestrian areas: maintain visibility at lower Eh with higher S/P spectra;
- Night tourism/landscape: reduce ecological and circadian disruption while preserving visual storytelling.
3. Five Indoor Scenarios: From “Style” to “Human Timeline”
1. Hotels
- Beyond “looks + Instagrammable”: guide lighting along the full day: check-in → hygiene → sleep → night wake → morning.
- Example:
- Arrival: slightly high Eh/Ev, neutral or slightly cool;
- 1–2 hours before sleep: lower Eh, Ev, and color temperature;
- Night wake: very low Eh + soft guiding light.
2. High-end residences
- Children’s rooms: task lighting meets Eh, Ev protects eyes and rhythm;
- Master bedroom: promote sleep, reduce Ev at night;
- Living/dining: support social, relaxation, occasional work—don’t apply one-size-fits-all.
3. Offices
- Open plan, meeting rooms, focus zones, relaxation areas: tailored Eh/Ev/CCT/contrast strategies;
- Collaboration with HR, ESG, or wellness teams, not just MEP.
4. Healthcare
- Patient rooms: daytime Ev supports alertness, nighttime is soft and non-disruptive;
- Nurse stations: maintain vigilance without overstimulation;
- Rehabilitation: support mood and motivation, not just “brighter is better.”
5. Education
- Classrooms, libraries, dorms, activity areas: design circadian rhythm for focus, rest, and social activity.
Key principle: draw a “human timeline” for each scenario—what state people should be in, and how light helps achieve it.
4. From Indoor to Outdoor: HCL in Urban and Infrastructure Lighting
Outdoor is a key part of daily light exposure—often overlooked.
- Urban landscapes & night tourism
- Problem: overlit plazas, cold color temperatures, long-term rhythm disruption, ecological impacts.
- Solution: use S/P ratio to maintain visibility while lowering Eh; design Ev at pedestrian eye level; gradually reduce brightness and color temperature at the end of routes (“wind-down”).
- Tourism lighting
- Beyond storytelling: create a “return-home curve” in lighting.
- Dramatic early scenes, gradual reduction later to prevent physiological overstimulation.
- Bridges & tunnels
- Already consider “entrance adaptation, mid-section illuminance, glare.”
- HCL adds: reduce fatigue, support circadian rhythm; segment tunnels/bridges with Ev, signage, and glare management.
5. AI + IoT: Making HCL Operational
Design stage: AI can generate multiple “human-centered scenarios,” optimizing Eh/Ev/S-P/m-EDI, freeing designers from repetitive calculations.
Implementation & operation: IoT sensors (occupancy, daylight, temperature, noise, CO₂) allow lighting systems to automatically adjust HCL scenarios, with regular calibration against design values.
Takeaway: AI and IoT don’t replace designers—they empower designers to manage truly “living” lighting environments.
6. Conclusion: HCL Is a Professional Upgrade
- Light is no longer just “visibility”—it’s about how it interacts with humans over time.
- Designers must learn: Eh, Ev, m-EDI, S/P ratio, rhythm models; adopt a human timeline; work with AI, IoT, and measurement tools.
- Opportunity: transition from “lighting stylist” to “lighting & wellness experience designer”, engaging clients on sleep, efficiency, brand, and urban nightlife.
Next project challenge: add one page to your design plan:
- Does Eh support tasks?
- Does Ev support circadian rhythm and mood?
- Is your lighting merely “pretty,” or already responsible?
English 
Chinese (Taiwan) 
Chinese (China) 
German