Human-Centric & Circadian Lighting
Design light around spectrum, intensity, timing, and the people who experience it.
Human-centric lighting is not a product category or a tunable-white setting. It is a design methodology that considers spectrum, light at the eye, timing, daylight, and controls as one system.
What Human-Centric Lighting Actually Means
Most of what is sold as "circadian lighting" is a single feature — usually a color-temperature slider. Yuji Lux takes a different position: we do not sell circadian lighting as a single product. We help designers engineer the spectrum, intensity, timing, daylight interaction, and controls required for a human-centric lighting strategy.
That means treating light as something people are exposed to over a whole day — not only something a room is finished with. The framework below is how we break that down on real projects.
The Human-Centric Lighting Framework
1
Spectrum
What wavelengths are actually present in the light? Two sources with the same color temperature can have very different spectral compositions — and very different visual and non-visual effects.
2
Intensity at the Eye
Horizontal workplane lux is not the whole story. The exposure that matters biologically is the light reaching the eye — which depends on fixture placement, optics, surfaces, and viewing geometry.
3
Timing
The same light can serve a different role depending on when it is delivered. Bright, high-melanopic light supports the day; the same spectrum in the late evening works against it.
4
Daylight
Electric lighting should be designed together with available daylight rather than treated as an isolated system — daylight remains the strongest and most efficient circadian signal.
5
Controls
The intended light exposure has to actually occur through the day. Spectrum, intensity, and timing need to be coordinated by controls and scheduling — not left to a wall switch.
Designing the Day
Light requirements change throughout the day. The following values are reference points from current circadian-lighting research and expert consensus (Brown et al. 2022) — framed for healthy adults with regular daytime schedules, not as universal targets for every population, space type, or project.
Morning
Prioritize strong light exposure
Daylight outdoors is ideal. During dark mornings, bright, high-melanopic electric light at eye level helps increase daytime light exposure when natural daylight is unavailable.
Day
≥250 lux melanopic EDI at the eye
The daytime reference level from the Brown et al. 2022 expert consensus. Most interiors fall well short of it — spectrum and light at the eye decide whether a space can reach it comfortably.
Evening
≤10 lux melanopic EDI, at least 3 h before bed
Shift to warm, dim, low-melanopic light in the pre-sleep hours, starting at least 3 hours before habitual bedtime.
Night
Darkness, with minimal warm light
Sleeping environments should be as dark as practical; where light is needed for navigation, keep it minimal, warm, and low.
Measure What Matters
Spectral Power Distribution (SPD)
The curve that shows what wavelengths are actually present in a light source — the starting point for every other metric, visual or biological.
Explore spectra in the Spectrum Designer →Melanopic EDI
Melanopic Equivalent Daylight Illuminance describes melanopic light exposure referenced to daylight — the metric used in circadian recommendations and WELL v2.
How melanopic EDI is measured →Melanopic DER
The melanopic Daylight Efficacy Ratio shows the melanopic effectiveness of a source relative to its photopic output — how "daylight-like" a spectrum is per lux.
Metrics in the Circadian Lighting Guide →Standards & References
Human-centric lighting projects may be evaluated against different scientific references, building standards, and project-specific requirements. Yuji Lux can help translate those requirements into measurable spectral and lighting targets.
CIE S 026
The international standard defining melanopic metrics — melanopic EDI and DER — and how they are calculated from a spectrum.
Brown et al. 2022
Peer-reviewed expert consensus (PLOS Biology) with reference daytime, evening, and night-time melanopic light levels for healthy adults with regular daytime schedules.
WELL Building Standard
A building certification framework whose light concept includes circadian-lighting design criteria based on melanopic metrics.
Project-specific criteria
Owner requirements, healthcare or hospitality briefs, and jurisdictional requirements that shape what a given project must achieve.
Tools
Seasonal
Winter Light Protocol
Are occupants actually getting enough daytime light during the darker months? A daylight-deficit calculator for any latitude, plus a practical, research-based winter lighting protocol.
Explore the Winter Light Protocol →Spectral
Spectrum Designer
Mix LED die and phosphor spectra and watch CCT, Duv, and CRI update live — an interactive way to explore how spectral composition drives every metric on this page.
Open the Spectrum Designer →More lighting tools: CRI Comparison Tool — color rendering, computed from real spectra.
Spectral Building Blocks
Yuji Lux provides spectral platforms that can be integrated into a human-centric lighting strategy.
SunWave™
Daylight-oriented, broad-spectrum illumination for daytime applications — high melanopic efficacy at high color quality.
Tunable White
A flexible platform for changing CCT and output throughout the day as part of a circadian lighting strategy.
Dim-to-FlameWarm™
Ultra-warm spectral transition for low-melanopic evening lighting applications.
A human-centric lighting strategy depends on the complete system: spectrum, output, optics, placement, daylight, controls, and schedule. Yuji Lux supplies the spectral sources and custom spectra, with technical guidance for integration with appropriate third-party US-certified drivers and controls.
Applications & Projects
Aerospace
Circadian Lighting for Aerospace
Spectrum engineering and dynamic lighting for an occupant environment with demanding technical requirements and full system integration.
View project →Hospitality
DRINKIT Coffee
Lighting scenes that change through the day, integrated into the architectural experience of a West Hollywood coffee bar.
View project →Knowledge Library
Foundations
Metrics & Spectrum
Applications & Seasons
Circadian Lighting in Healthcare, Hospitality & Transportation
Where circadian design requirements show up in real briefs.
FlameWarm™: Low-Melanopic Warm Spectrum
Evening and hospitality lighting with minimal melanopic content.
Why Winter Wrecks Your Energy
The light-deprivation math behind the seasonal slump.
Frequently Asked Questions
What is human-centric lighting?
A design methodology that considers spectrum, light at the eye, timing, daylight, and controls as one system — accounting for both the visual and the non-visual (circadian) effects of light on the people in a space. It is not a product category or a single fixture setting.
Is tunable white the same as circadian lighting?
No. Tunable white is a platform for changing CCT and output through the day. A circadian strategy also depends on spectrum, light reaching the eye, fixture placement, daylight, controls, and scheduling — tunable white can be part of it, but does not constitute it by itself.
What is melanopic EDI?
Melanopic Equivalent Daylight Illuminance — a CIE S 026 metric that describes the melanopic (circadian-relevant) light exposure of a source or a space, referenced to daylight. It is the metric used in the Brown et al. 2022 consensus recommendations and in WELL v2.
How much light is needed during the day?
The Brown et al. 2022 expert consensus recommends at least 250 lux melanopic EDI at the eye throughout the daytime, as a reference point for healthy adults with regular daytime schedules. Individual projects, populations, and space types may have different requirements.
Can standard architectural lighting support a circadian strategy?
Often only partially. Typical static warm-white interiors deliver melanopic levels far below daytime reference values, and cannot shift down for the evening. Whether a lighting scheme supports a circadian strategy is decided by spectrum, light at the eye, daylight integration, and controls.
Does Yuji Lux provide complete circadian systems or spectral components?
Yuji Lux provides spectral LED platforms — linear LED sources, custom-engineered spectra — plus technical guidance for integrating them with appropriate third-party US-certified drivers and control systems. System design, controls, and scheduling are delivered together with the project team.
Can Yuji Lux engineer a custom spectrum for a project?
Yes. Custom spectral engineering is a core capability: starting from target metrics — melanopic DER, CRI and R9, CCT and Duv — through spectral design to production.
Designing a human-centric lighting project?
Tell us about the space — our engineering team can help translate your project's requirements into measurable spectral and lighting targets, and specify the sources to meet them.