The issue is not just the hardware. It is the DLMO logic.
Abstract
This article examines how LED component makers, luminaire manufacturers, control system providers, and lighting designers can build truly effective circadian lighting by following DLMO logic. It argues that the real challenge is not isolated parameters, but cumulative dose, eye-level delivery, and outcome validation.
Over the past few years, more and more companies have started talking about circadian lighting, sleep lighting, and healthy light.
But if we return to the underlying logic of DLMO — Dim Light Melatonin Onset — we quickly realize something important: truly effective circadian lighting is not simply about making light cooler during the day, warmer at night, or adding tunable white and dynamic scenes.
The real issue is this:
What kind of total light exposure does a person receive over the course of a day, at the eye, in the right timing windows, and does that exposure actually change physiology and behavior in a meaningful way?
That is why I increasingly believe that the next real competition in circadian lighting will not be about who can tune more parameters. It will be about who can build an integrated solution around hardware + scenes + cumulative dose + validation.
1. Why DLMO changes the definition of circadian lighting
DLMO matters because it does not simply describe whether someone sleeps well.
It helps answer a more fundamental question:
When does the body’s internal night actually begin?
In sleep medicine and circadian science, DLMO is widely used as a key phase marker of the central circadian clock, and it is often used to optimize the timing of bright light and melatonin interventions. Melatonin typically begins to rise about 2–3 hours before habitual sleep onset, and DLMO marks that transition.
This means circadian lighting should not be defined merely as “healthy-looking lighting.”
It should be judged by whether it can answer questions like:
- Does it provide enough effective circadian stimulus during the day?
- Does it reduce stimulation at the right time in the evening?
- Does it avoid suppressing melatonin when the body is preparing for sleep?
- Does it help stabilize or shift circadian phase in the intended direction?
In other words, the true objective is not a single snapshot parameter.
It is the daily exposure trajectory.
I prefer to summarize this in two words: cumulative dose.
2. The most common reason circadian lighting fails: it ignores cumulative dose
When companies discuss circadian lighting, the first things they usually mention are:
- spectrum
- CCT
- dynamic dimming
- pre-set scenes
All of these matter. But on their own, they are not enough. The circadian system does not decide its response from a single glance.
It is shaped by accumulated time cues across the day:
- Was morning light strong enough and early enough?
- Was daytime exposure sustained and effective?
- Did stimulation drop at the right time in the evening?
- Was night-time exposure sufficiently reduced, or was the system repeatedly disturbed?
The 2022 expert recommendations in PLOS Biology clearly state that healthy adults should receive relatively high melanopic EDI during the day, significantly lower levels in the 3 hours before bedtime, and as little as possible during sleep. These recommendations are based on vertical eye-level exposure, not just workplane illuminance.
The industry implication is clear: Circadian lighting cannot stop at “what is the fixture doing right now?”
It also has to answer:
- How much effective circadian stimulus did this user actually receive today?
- In which timing windows did it occur?
- Was there unnecessary stimulation at the wrong time?
- Is the total exposure profile supporting entrainment, phase advance, maintenance, or disruption?
If a company cannot answer these questions, then many so-called circadian lighting solutions are still just adjustable white lighting.
3. What LED component makers need to upgrade first
Some people think DLMO is far removed from LED package manufacturers.
I think the opposite.
If the upstream logic does not evolve, the downstream ecosystem will struggle to build truly effective circadian solutions.
1) Move from “efficacy + CCT + CRI” to a dual visual + non-visual language
Most LED data sheets still focus on:
- efficacy
- CCT
- 比显指
- binning
- lifetime
- electrical performance
These remain essential. But they are no longer sufficient for the circadian era.
Upstream suppliers should increasingly provide:
- spectral power distribution
- melanopic / α-opic relevant quantities
- non-visual performance under different spectral mixes
- spectral stability under dimming
- circadian consistency under different drive conditions
Because designers and control platforms are no longer just creating white light.
They are building time-based light recipes.
If LED suppliers cannot provide stable, traceable, and model-friendly spectral information, downstream players will struggle to implement circadian strategies with precision.
2) Move from “one universal LED” to “programmable spectral capability”
The future is not about one fixed optimum point. It is about spectral combinations that can be shifted over time, with predictable non-visual impact.
That means component makers should begin thinking in terms of:
- spectral mixes suited for morning phase-advancing stimulus
- daytime performance-supportive stimulus
- evening wind-down modes
- low-disruption night pathways
That is no longer the traditional logic of selling a light source. It is the beginning of selling a programmable circadian foundation.
4. What luminaire manufacturers must really do: deliver dose to the eye
Circadian lighting does not happen on a specification sheet. It happens at the human eye.
So for luminaire manufacturers, the real challenge is not just enabling tunable white.
It is ensuring that the intended dose reaches the eye in a controllable and useful way.
1) Move from plane-based lighting to eye-level lighting
Circadian effectiveness is more closely related to actual eye exposure than to horizontal workplane illuminance. The major recommendations increasingly emphasize melanopic exposure at the eye.
This means luminaire design must increasingly consider:
- optical direction
- emitting surface position
- the balance between glare control and effective circadian delivery
- direct / indirect / semi-indirect proportions
- seated, standing, and reclined eye positions
简而言之： The goal is not just to illuminate the room. It is to deliver the right circadian dose to the eye.
2) Move from one luminaire logic to time-based luminaire roles
A more mature circadian lighting system may not rely on one luminaire doing everything.
Instead, it may include:
- stronger morning/daytime stimulus luminaires
- transitional evening luminaires
- low-disruption night luminaires
- bedroom or hotel pathway lighting
- dual-logic luminaires for care tasks versus rest protection
This is especially important in real-world environments. Research in ICU settings shows that visual task needs and circadian goals are not naturally aligned, and that dynamic, zoned, and time-based solutions are more realistic than static ones.
For luminaire companies, this means product families should move from “selling by room type” to “selling by time-task logic.”
5. Why control systems matter more than ever
I have said this for years: in the HCL and circadian era, control systems will be revalued.
Because circadian lighting is not fundamentally a static hardware problem.
It is a time orchestration problem.
1) Move from scene switching to circadian scripting
Traditional control systems are mostly valued for:
- scheduling
- dimming
- CCT control
- occupancy sensing
- energy savings
- scene recall
But once we apply DLMO logic, the system has to answer more:
- When should the morning stimulus begin?
- How quickly should it ramp?
- How should daytime cumulative dose be maintained?
- When should evening reduction begin?
- How should night-time visual needs be preserved while minimizing circadian disruption?
This is no longer just “having scenes.”
It is building physiology-aware time scripts.
2) Control systems must begin to account for cumulative exposure and feedback
This is one of the biggest future dividing lines.
Advanced circadian controls should not only know the current output value.
They should increasingly be able to:
- estimate cumulative effective exposure over time
- adjust electric light based on daylight contribution
- respond to occupancy and activity type
- estimate real user exposure
- calibrate strategy with measurements and feedback
In other words, the system should know more than “the room is currently 4000 K and 300 lux.”
It should increasingly understand: How much useful daytime signal has this person already received today, and how much circadian margin remains for the evening?
That is a much more DLMO-aligned system logic.
6. Designers are becoming “time experience orchestrators”
If LED component makers define the spectral raw material, luminaires determine delivery, and control systems determine temporal behavior, then designers ultimately determine how all of this becomes human experience.
This is why I believe the role of the designer is being fundamentally upgraded.
1) Design must move beyond “how bright and how beautiful”
It must also ask:
- At what time should this space support alertness?
- At what time should it support restoration?
- At what time must stimulation be reduced?
- Do different users in the same space have different circadian needs?
- How do visual comfort, operations, maintenance, and circadian goals coexist?
That changes the design starting point.
2) Designers must move from parameter thinking to exposure trajectory thinking
The strongest designers in the next phase will not only specify:
- 3000 K / 4000 K
- 300 lx / 500 lx
- UGR / CRI
They will increasingly specify:
- 7:00–9:00: rapid morning stimulus build-up
- 10:00–15:00: sustained daytime signal
- after 18:00: marked reduction in eye-level melanopic exposure
- after 22:00: only low-disruption pathway lighting
- distinct strategies for bed, desk, social, washroom, and transit activities
That is much closer to a DLMO-aware design language.
7. Hardware and scenes must be designed together
Many companies still follow this sequence: First build the product.
Then look for a “healthy lighting” use case. In circadian lighting, that order is often backwards.
A more appropriate logic is: Define the scene objective first, then define the hardware requirement
Scene 1: Office
The goal is not simply high illuminance.
It is sufficient daytime stimulus, limited evening carry-over, and good visual performance.
That leads to hardware needs such as:
- strong morning/daytime eye-level exposure
- 日光协同
- low glare without losing useful stimulus
- spectral and control capability for evening reduction
Scene 2: Bedroom / Hotel
The goal is not to create a “sleep lamp” gimmick. It is to reduce melatonin suppression opportunities while preserving necessary function.
That leads to hardware needs such as:
- very low-disruption night lighting
- low-stimulus bathroom and pathway lighting
- evening transition modes
- morning wake-up modes
Scene 3: Healthcare / Senior living / Wellness
The goal is to balance care tasks, resident rest, and staff circadian needs.
That means hardware and controls must support:
- zoning
- scheduling
- role-based logic
- task-based logic
- traceable validation
So future circadian lighting products cannot be defined independently of scenes.
Hardware must be designed for the scene, and the scene must be supported by the hardware.
8. Why I keep emphasizing validation
Because one of the biggest risks in this field is that many claims sound persuasive, but the outcomes may not be real.
From a DLMO perspective, circadian lighting should not be judged only by whether it is dynamic.
It should be judged by whether it changes the intended outcome.
At least three layers need validation
1) Output validation
Is the system actually delivering what was designed?
- actual SPD
- actual illuminance
- actual eye-level exposure
- actual time profile
- actual stability across dimming and tuning
2) Dose validation
Did the user actually receive the intended cumulative dose?
- enough morning stimulus?
- enough daytime accumulation?
- timely evening reduction?
- sufficiently low night-time exposure?
3) Outcome validation
Did that exposure trajectory actually change anything meaningful?
- alertness
- comfort
- sleep quality
- circadian stability
- task performance in target applications
This is why the ICU dynamic lighting study is valuable. It did not stop at comparing lighting configurations. It also looked at visual comfort and biological markers such as melatonin and cortisol. The authors rightly note the sample-size limitations, but the direction is important:
circadian lighting ultimately has to return to outcomes.
9. Why validation toolchains matter
If the industry is serious about cumulative dose and real outcomes, we can no longer rely only on intuition and one-off impressions.
That is one reason we have continued building the In.Licht toolchain.
In.Licht Pro
Better suited for field diagnosis, inspections, and practical project communication.
It helps teams see the basic light facts more clearly.
In.Licht Ultra
Better suited for R&D, quality control, comparison, and deeper spectral analysis.
It helps teams understand why two lights that look similar may behave very differently.
In.Licht Well
Better suited for continuous monitoring and operational management.
It helps move from “measure once” to long-term optimization, integrating EML, M-EDI, and broader environmental factors into one workflow.
Together, they support a much more useful workflow: see the facts → understand the mechanism → build cumulative dose logic → validate → optimize
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10. Who will win next?
I increasingly believe that the winners in the next phase will not simply be the companies that talk most about HCL or healthy light.
They will be the ones that build real capability around:
- programmable and model-ready spectral foundations
- luminaires that deliver dose effectively to the eye
- control systems that orchestrate physiological timing
- design methodologies that integrate time, space, and activity
- field workflows that measure, validate, and improve continuously
At the center of this are two ideas:
cumulative dose
outcome validation
The companies that can build products and projects around those two ideas will be much closer to the real value of next-generation circadian lighting.
Conclusion: circadian lighting is not just another mode
If we rethink the industry through the lens of DLMO, we see that circadian lighting is not simply a new “sleep mode” added to conventional lighting.
It is a more fundamental shift:
- LED components become the foundation of temporal light recipes
- luminaires become dose delivery devices
- controls become time orchestration systems
- design becomes time experience design
- validation becomes outcome validation, not just brightness checking
That is how I understand circadian lighting.
And that is why I believe the real future value lies not in one isolated product, but in a methodology that integrates:
hardware + scenes + cumulative dose + effect validation
That, in my view, is one of the most important directions for the next upgrade of our industry.
Call-to-Action
如果你是
- an LED component maker
- a luminaire manufacturer
- a control system platform
- a lighting designer or consultant
- or a brand exploring circadian lighting for offices, hotels, residential, wellness, healthcare, or senior living
I would be glad to connect.
At 光配方研究院（Lighting Recipe Studio, LRS）, we are interested in working with partners on:
- DLMO-based product definition for circadian lighting
- scene scripting based on cumulative dose logic
- integrated R&D, measurement, and validation workflows
- joint development from concept to real-world deployment
Because circadian lighting should not just be dynamic.
It should be effective.
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