A nine-site study found 24.0% of daytime minutes reached 250 lx melanopic EDI. What the measurements show, how 75 lx is misread, and five spec clauses.
The short answer. Two documents now describe the same problem from opposite ends. The Society of Light and Lighting (SLL) published its Position Statement on Integrative Lighting in August 2026 and adopted the CIE principle of bright days and dark nights, with a daytime condition of at least 250 lx melanopic EDI at the eye. A nine-site wearable study by Zauner and colleagues, posted as a preprint in 2026, measured what people actually receive. Only 24.0% of recorded daytime minutes reached the 250 lx recommendation. Site-average melanopic EDI was 198.8 lx for indoor daylight, 85.1 lx for indoor electric light and 959.6 lx outdoors. A lighting specification cannot change what people do with their day. It can change what the room delivers when they are in it, and it can put the number on paper at handover. That is the whole of the claim this article makes.
Five findings carry the argument.
What this changes for a person buying lighting. The informative number for a room is not the melanopic-to-photopic ratio of a luminaire. It is the vertical melanopic EDI at eye level, during occupied hours, with the controls doing what the design says they do. Those two quantities are connected, but only through geometry, surface reflectance, daylight and time. A specification can require the first quantity to be measured, and can require the second to be supplied. It cannot require an occupant to receive a health outcome, and this article does not claim one.
What the buyer can do on the next project. Put five clauses into the lighting specification: an eye-plane vertical melanopic EDI condition instead of a desk-plane lux figure; a stated melanopic efficacy for every source in the schedule; a daylight-first sequence before any electric load is added; verification at the dimmed states the evening actually uses; and a handover measurement report with the instrument and the calibration stated. §D.8 sets out the five clauses. §D.9 works through the arithmetic that makes them hard, including the energy ceiling that stops a designer from simply raising the output.
| # | Fact | Number | Primary source |
|---|---|---|---|
| 1 | Daytime consensus condition for melanopic EDI at the eye | at least 250 lx, continuous across occupied daytime | Brown et al. (2022), endorsed in CIE PS 001:2024, restated in SLL position statement, August 2026 |
| 2 | Evening condition, three hours before intended sleep | no more than 10 lx melanopic EDI | Same chain; SLL position statement, August 2026 |
| 3 | Sleep condition | no more than 1 lx melanopic EDI, target as close to 0 as possible | Same chain; SLL position statement, August 2026 |
| 4 | Share of recorded daytime minutes meeting the 250 lx recommendation | 24.0% (137,792 of 573,712 minutes) | Zauner et al., bioRxiv preprint, version posted 23 September 2026 |
| 5 | Work day versus free day, modelled adherence | 26.6% (95% CI 24.5 to 28.7) versus 21.5% (19.2 to 23.8) | Same preprint, Table 2 |
| 6 | Pre-sleep minutes within the evening condition | 63.3% (81,894 of 129,390 minutes) | Same preprint, results summary |
| 7 | Sleep-window minutes within the night condition | 87.7% (336,052 of 383,366 minutes), measured at the bedside | Same preprint, results summary |
| 8 | Site-average melanopic EDI, indoor electric light | 85.1 lx (95% CI 71.6 to 101.1) | Same preprint, September 2026 version, interaction model |
| 9 | Site-average melanopic EDI, indoor daylight | 198.8 lx (169.3 to 233.4) | Same preprint, September 2026 version |
| 10 | Site-average melanopic EDI, outdoor daylight | 959.6 lx (786.8 to 1,170.2) | Same preprint, September 2026 version |
| 11 | Same three estimates in the June 2026 version | about 75 lx, about 172 lx, about 707 lx | Same preprint, version posted 16 June 2026; the figures the SLL statement reports |
| 12 | Ratio of outdoor to indoor-electric site averages | 11.27 | Same preprint, September 2026 version; the ratio as stated there, computed from unrounded estimates |
| 13 | Setting averages | outdoors 714.2 lx; office or home work 198.9 lx; awake at home 76.4 lx; sleep 4.28 lx | Same preprint, September 2026 version |
| 14 | Median daily geometric mean melanopic EDI | 5.154 lx (IQR 2.831 to 9.225) | Same preprint, Table 3 |
| 15 | Median mean of the brightest 10 hours | 110.566 lx (IQR 41.513 to 243.212) | Same preprint, Table 3 |
| 16 | Median time above 250 lx melanopic EDI while awake | 2.417 h (IQR 0.850 to 4.617) | Same preprint, Table 3 |
| 17 | Median melanopic daylight efficacy ratio of measured light | 0.724 (IQR 0.643 to 0.795) | Same preprint, Table 3 |
| 18 | Variation among people and days within sites versus between sites | ratio 1.99 (95% CI 1.29 to 4.77) | Same preprint, results summary |
| 19 | Study design | 191 adults on the roster, nine sites in seven countries, 1,478 recorded participant-days; near-eye sample 141 participants and 816 screened days; loggers sampling every 10 s; collection August 2023 to October 2025 | Same preprint, methods and Table 1 |
| 20 | Status of the SLL document | position statement, not a design standard (the document's own words, page 1) | SLL position statement, August 2026 |
| 21 | Maximum allowable lighting power density, office space above 200 m² | 7.2 W/m² (BEC 2024, Table 5.4) | EMSD Code of Practice for Energy Efficiency of Building Services Installation (BEC 2024) |
Terms and units used below. Melanopic EDI (melanopic equivalent daylight illuminance) = the illuminance of CIE standard illuminant D65 that would produce the same melanopic stimulus as the light being measured, in lux; the quantity is defined in CIE S 026:2018. MDER = melanopic daylight efficacy ratio, the ratio of melanopic EDI to photopic illuminance for a given spectrum, dimensionless. m-EDI = the short form of melanopic EDI used on the science page. M/P ratio = melanopic-to-photopic ratio, the shorthand SUMLINK publishes for the same relationship at a stated condition. ipRGC = intrinsically photosensitive retinal ganglion cell. CCT = correlated colour temperature, in kelvin. SLL = Society of Light and Lighting, part of CIBSE. CIE = International Commission on Illumination. BEC = Building Energy Code (Hong Kong). CI = confidence interval. IQR = interquartile range. lx = lux. A preprint is a manuscript posted before peer review; it is cited here as a preprint, not as a peer-reviewed paper.
The SLL document is a 13-page position statement written by Dr Cosmin Ticleanu of BRE and published in August 2026. It replaces the Society's July 2020 position statement on circadian lighting. That replacement carries a terminology decision that matters to anyone writing a specification: the Society adopts the CIE term integrative lighting, defined in the CIE International Lighting Vocabulary (CIE S 017:2020), and notes that circadian lighting, human-centric lighting and biodynamic lighting are industry usage rather than official CIE terms.
The document is explicit about its own weight. It states that it is a position statement and not a design standard, in those two words on page 1. That sentence is the reason this article quotes it as authority for principle and not for numbers to be copied into a tender. The numbers in the document come from a named evidence chain, and the chain is short enough to follow: the consensus recommendations of Brown et al. (2022), documented in CIE TN 015:2023, endorsed in CIE PS 001:2024 (third edition, August 2024).
The central principle is stated in one line: "The central organising principle is simple: bright days, dark nights." Daylight is the primary means of delivering daytime melanopic exposure, and electric lighting is described as a complementary tool for the cases where daylight is unavailable, insufficient or poorly distributed.
Three statements in the document are directly useful when a supplier's claim has to be tested.
The document also carries the caution that keeps the whole field honest, quoting Dr Peter Boyce's 2016 editorial: the further an outcome sits from the direct physiological effect of light, the more likely it is that factors other than lighting intervene. For a commercial lighting supplier, that sentence is not a threat. It is the boundary that makes a specification defensible: the supplier is accountable for the delivered light condition, and for nothing beyond it.
One more element of the document deserves attention because it is easy to skip. The Society warns against using integrative lighting as a justification for raising installed electric load. Increasing daytime melanopic exposure, it says, should not be pursued by adding installed lighting power where daylight, layout, surface reflectance, controls or a more efficient spectrum can achieve the same purpose. A systematic review of the energy impacts of integrative lighting by Taghizadeh et al. (2025) is cited for the finding that poor schemes raise energy consumption when non-visual objectives are addressed only by adding more electric light. That finding is what connects this article to the energy code in §D.9.
The measurements come from MeLiDos, a prospective multicentre observational field study with a harmonised protocol. The design is worth stating in full, because the strength and the limits of every number in this article follow from it.
Two cautions in the paper are worth repeating in a specification context. The near-eye position, in the authors' words, "measures light closer to the eye but is not a direct retinal measurement". And the authors note that "very low readings require caution" — which matters because the sleep and morning figures in this dataset sit in the region where instrument error is largest relative to the value.
The headline result is precise. In the September 2026 version: exposure was within the applicable recommendation during 24.0% of daytime minutes, 63.3% of pre-sleep minutes and 87.7% of sleep minutes. In counts, that is 137,792 of 573,712 daytime minutes, 81,894 of 129,390 pre-sleep minutes and 336,052 of 383,366 minutes during reported sleep.
The paper then adds the sentence that most secondary reporting drops: "These pooled-minute percentages describe how often exposure lay within range, not participant adherence." The unit is the minute, pooled across participants and days. A person who spent ninety minutes in bright daylight and six hours in a dim office contributes both kinds of minute.
The modelled comparison by day type is a separate analysis: 26.6% (95% CI 24.5 to 28.7) on work days against 21.5% (19.2 to 23.8) on free days. The work-day figure is higher, which runs against the assumption that offices are the dimmest part of a week; the paper's setting estimates in §D.5 show why, and they are worth reading before that assumption is repeated in a sales deck.
There are three ways this number gets misused, and each one changes what a buyer would do.
Misread one — 24% of people comply. The fraction counts minutes, not people. A compliance rate by participant is not reported as the headline figure, and the paper explicitly separates the two concepts. A supplier quoting this figure as a user-adoption statistic has changed the unit.
Misread two — 24% of waking time, so the problem is the working day. The daytime window in this analysis excludes the three hours before reported sleep, and it is not a work schedule. The pre-sleep and sleep fractions show the other half of the same distribution: 63.3% of pre-sleep minutes met the evening condition, which means more than a third did not.
Misread three — the target is 250 lx, so 24% is a lighting failure. The recommendation is a condition to be supported across occupied daytime, and the SLL is explicit that it is not a dose to be hit once. A room can pass a spot measurement and still deliver a dim day, because the occupant's minutes include corridors, meeting rooms, transport and home. That is not an argument that lighting design does not matter. It is an argument that a design claim expressed in desk-plane lux cannot answer a question measured at the eye.
One average of a day tells you almost nothing about what the day contained, and the preprint therefore reports a family of metrics rather than a single score. The authors state that these features are not interchangeable health-response estimates, which is a useful discipline for anyone building a product claim on them.
| Metric | What it describes | Median (IQR) in the dataset |
|---|---|---|
| Mean melanopic EDI | geometric average of daily melanopic EDI values, including zeros; overall exposure with peak influence reduced | 5.154 lx (2.831 to 9.225) |
| Brightest 10 h mean | strength of the main daytime light episode | 110.566 lx (41.513 to 243.212) |
| Darkest 10 h mean | the dark half of the cycle, relevant to the evening and night condition | 0.103 lx (0.020 to 0.253) |
| Time above 250 lx melanopic EDI while awake | duration of exposure at or above the daytime recommendation | 2.417 h (0.850 to 4.617) |
| Time above 1,000 lx melanopic EDI | duration of high-level daytime exposure | 0.683 h (0.183 to 1.558) |
| Melanopic daylight efficacy ratio | spectral composition relative to photopic illuminance | 0.724 (0.643 to 0.795) |
Read the first row against the second. The daily geometric mean is 5.154 lx because the average includes the dark hours at the two ends of the day. The mean of the brightest ten hours is 110.566 lx. Both describe the same participants, and neither contradicts the other. A claim that quotes one of them without saying which is being quoted is not a measurement claim.
The duration row is the one that a specification can act on. A median of 2.417 hours above 250 lx means the middle participant accumulated a couple of bright hours, usually by going outside, and spent the rest of the waking day below it. The SLL's position on the daytime condition is precisely that this pattern — a bright episode inside a dim day — is not the recommendation.
The last row deserves its own note because it is the bridge to procurement. A median MDER of 0.724 describes the mixed light these people actually sat in: daylight through glazing, LED office lighting, screens, and the mixture of the three. It is not a product property, and it should not be read as one. It is, however, the number that converts a photopic vertical illuminance into a melanopic one in a field condition, and §D.9 uses it for exactly that purpose.
The preprint models site-average melanopic EDI by reported light source and by setting. The estimates are model results with 95% confidence intervals, not raw means, and they are the most decision-relevant numbers in the paper for a lighting specification.
| Source or setting | Site-average melanopic EDI (lx) | 95% CI |
|---|---|---|
| Outdoor daylight | 959.6 | 786.8 to 1,170.2 |
| Indoor daylight | 198.8 | 169.3 to 233.4 |
| Indoor electric light | 85.1 | 71.6 to 101.1 |
| Screen light | 23.8 | 17.4 to 32.5 |
| Setting: outdoors | 714.2 | 561.7 to 908.2 |
| Setting: office or home work | 198.9 | 173.9 to 227.5 |
| Setting: on the road or in a vehicle | 331.2 | 274.4 to 399.8 |
| Setting: awake at home | 76.4 | 62.0 to 94.1 |
| Setting: sleep (bedside) | 4.28 | 3.06 to 5.99 |
Outdoor daylight is 11.27 times the indoor electric estimate. That is the preprint's own ratio. It comes from the unrounded model estimates, so dividing the two rounded figures printed above gives 11.28, not 11.27. That single ratio explains the shape of the whole problem: the day is bright when a person is outside it, and the indoor environment is where the dim hours happen. It also explains why an office lighting specification cannot close the gap on its own, and why the SLL puts daylight first and treats electric light as support.
The setting row that surprises people is the workplace. At-work exposure averages 198.9 lx, below the 250 lx condition but far above the at-home figure of 76.4 lx. An office that already has decent windows and a reasonably lit interior delivers more melanopic stimulus than the same person's evening at home. This is why the work-day adherence figure in §D.3 exceeds the free-day figure, and it is also why an office refurbishment aimed at nighttime comfort — lamps that dim to a low melanopic output in the evening — is a different product decision from a daytime condition target.
The screen estimate, 23.8 lx, is worth stating plainly because screen-based claims are common. A display close to the face contributes a small amount of melanopic stimulus at the eye compared with daylight, and the paper's model puts it in that position.
The figure that has travelled furthest into trade material is 75 lx. The SLL position statement reports the study's averages as approximately 75 lx under indoor electric lighting, 172 lx under indoor daylight and more than 700 lx outdoors. Those are the estimates in the version of the preprint posted on 16 June 2026.
The version posted on 23 September 2026 carries a revised title and revised model estimates. The indoor electric estimate is 85.1 lx, the indoor daylight estimate 198.8 lx and the outdoor estimate 959.6 lx, each with a confidence interval. The direction of the finding does not change. The magnitudes do, by between 13 and 36% depending on the category.
| Version | Title | Indoor electric | Indoor daylight | Outdoor daylight |
|---|---|---|---|---|
| Posted 16 June 2026 | Environmental and behavioural determinants of the personal light exposome | about 75 lx | about 172 lx | about 707 lx |
| Posted 23 September 2026 | The health-relevant architecture of the everyday light exposome | 85.1 lx (71.6 to 101.1) | 198.8 lx (169.3 to 233.4) | 959.6 lx (786.8 to 1,170.2) |
Three rules follow, and they are rules for our own copy as much as for anyone else's.
This article uses the September 2026 estimates for all measurements and reports the June figures only where the SLL comparison or the provenance of the 75 lx headline has to be explained. The 75 lx in the headline of this article is the figure that trade material already uses, and the article's job is to put it back in its proper frame rather than to keep it in circulation unqualified.
The SLL draws the conclusion from the measurements in one clause: the findings underline "the need to consider actual personal exposure at the eye, not design illuminance alone". This is the technical heart of the article, and it has three consequences.
Horizontal illuminance on a desk is not vertical illuminance at an eye. A workplace lighting design is normally verified on the horizontal working plane, because the visual task sits there. Melanopic EDI is assessed at the eye, which is a vertical or near-vertical plane at a different height, often facing a different direction, and frequently pointing at a wall, a window or a corridor rather than at the luminaire. The two quantities are related by the geometry of the room, not by a fixed factor. A design that hits its horizontal target therefore says nothing certain about the vertical eye-plane value, and a specification that only names the horizontal target has not specified the melanopic condition. See Human-centric lighting science: ipRGCs, m-EDI and CIE S 026.
Illuminance is not spectrum. Two sources delivering the same photopic lux can deliver different melanopic EDI. The conversion is the melanopic daylight efficacy ratio, and it is a property of the spectrum at the eye, which depends on the source, the surfaces, and the daylight mix. The SLL states the position directly: "CCT alone is insufficient and can be misleading". A warm-white or neutral-white descriptor is not a melanopic specification.
A design value is not a delivered value. Controls change the output during the day, occupants close blinds, and furniture moves. The preprint's own dispersion finding points the same way: "Variation among people and days within sites exceeded that among sites". In other words, what happens inside one room on different days is a larger source of difference than which city the room is in. A single commissioning measurement at full output on a sunny afternoon describes the best case in the dataset, not the condition a person receives.
There is a further limit that the SLL states about its own evidence and that a supplier should repeat rather than hide: the consensus applies to healthy young-to-middle-aged adults. Its applicability to older people, to people with visual or medical conditions and to shift workers requires further study, as identified in CIE PS 001:2024. A specification can be written for a defined population in a defined space. A marketing claim cannot.
The gap between 85.1 lx of indoor electric light and a 250 lx condition is a design problem, and design problems respond to clauses. The five below are written so that each one produces a document at handover, and so that each one can be checked by a third party without re-reading the design narrative.
Clause 1 — Name the quantity, the plane and the condition. State the requirement as melanopic EDI in lux, measured on a vertical plane at eye level, in the occupied zone, across defined occupied hours. Name the target and name the minimum duration within the occupied day. Do not state a horizontal lux figure and call it the melanopic condition, and do not accept a single spot measurement at one time of day as evidence of a condition.
Clause 2 — Require the spectral quantity for every source in the schedule. For each luminaire type, require the melanopic daylight efficacy ratio, or the melanopic-to-photopic ratio at a stated condition, from a test report rather than from a catalogue headline. Require the same field for the glazing where the daylight contribution carries the design, and require the daylight factor or the modelled vertical illuminance that supports the claim. Reject a schedule whose melanopic column reads "warm white" or "3000 K".
Clause 3 — Order the interventions: daylight, geometry, surface, spectrum, then power. The sequence matters because the SLL warns that integrative lighting should not be used to justify extra installed load. Require the design to demonstrate what daylight, room geometry, surface reflectance and controls deliver before the electric lighting power is set. Where the specification is comparative — one scheme against another — require the vertical eye-plane melanopic EDI and the lighting power density side by side in the same table.
Clause 4 — Verify at the states the space actually uses. Require measurement at full output, at the daytime dimmed state and at the evening state. The evening state is the one that is normally skipped, and it is the state where the SLL flags a second risk: dimmed operation can introduce temporal light modulation, and compliance assessed at rated output does not characterise performance across the dimming range. The Society suggests methods such as those in IEC TR 61547-1:2020 where low-light operation is critical. A specification that tests only full output has verified one of three states.
Clause 5 — Receive the handover measurement report. Require a report that names the instrument, its calibration date, its stated accuracy and the measurement positions on a plan, with the vertical eye-plane melanopic EDI at each position and the time and control state of the reading. A number without those four attachments is not a verification, it is a claim. The report is also the only artefact that makes the next refurbishment auditable, because it says what the room was delivering before the change.
What the five clauses do not do. They do not make a product integrative. They do not guarantee that occupants receive a health outcome, and they do not transfer responsibility for the room's daylight, layout or use. They convert a design intention into a measured condition with a named instrument and a date. In a market where several suppliers use the same vocabulary, that conversion is the difference between a specification and a slogan. See the Hong Kong office guide to human-centric lighting.
Two calculations sit between the consensus condition and a specification, and both are simple enough to put in a meeting.
The first calculation: what vertical photopic illuminance does the condition need? By definition, melanopic EDI equals the melanopic daylight efficacy ratio multiplied by the photopic illuminance at the same plane. Inverting that gives the vertical photopic illuminance required for a stated melanopic EDI at a stated MDER. The preprint's measured median MDER was 0.724.
| Case | MDER assumed | Vertical photopic illuminance for 250 lx melanopic EDI |
|---|---|---|
| Field median, measured mixed light (preprint) | 0.724 | 345 lx |
| Higher-melanopic source mix | 0.85 | 294 lx |
| Low-melanopic source mix | 0.60 | 417 lx |
Internal estimate. These three rows are arithmetic from the melanopic EDI definition using the preprint's median MDER and two illustrative ratios. They are not measurements and they are not a design prediction; a real project must measure the vertical plane, because daylight, surface reflectance and view direction set the value. What the table does establish is the scale: a 250 lx melanopic condition at the eye sits in the region of 300 to 420 lx of vertical photopic illuminance for the spectrum the field data recorded. That is a materially different requirement from a 500 lx horizontal desk target, and it is not satisfied by the desk target by default.
The second calculation: the energy ceiling. Hong Kong's Building Energy Code sets a maximum allowable lighting power density of 7.2 W/m² for office space with internal floor area above 200 m², and requires automatic lighting control for that space type. On a 1,000 m² office floor the ceiling is therefore 7,200 W of lighting power in total.
The two calculations meet here. If the vertical condition is pursued by raising electric output across the whole floor, the installed load has to stay under that ceiling, and the SLL's own guidance says that raising installed load is the wrong first move when daylight, layout, reflectance, controls or spectrum can do the work. That is not a health argument and it is not a wellness argument. It is a code argument, and it is the one that a building owner's consultant will run in the first design meeting.
The practical consequence for a specification is the ordering rule in clause 3: daylight and geometry first, spectrum and controls second, electric power last. A design that starts from the wattage and then looks for a melanopic number will either miss the condition or breach the ceiling, and often both.
A third number that is not arithmetic but matters for the brief. Between 6 pm and 10 pm, an office that dims to a low melanopic output is doing something different from an office that stays bright. The evening condition — no more than 10 lx melanopic EDI in the three hours before intended sleep — is a lighting control objective in any building that is occupied into the evening, and it is the state that clause 4 asks to be measured. In the dataset, 63.3% of pre-sleep minutes met that condition, so more than a third did not. A dimming schedule that exists on a drawing and not in a measurement belongs in that missing third until it is verified. See ISO/CIE 8995-1:2025 and melanopic EDI in the workplace standard.
This article argues for disciplined claims, so the same test has to be applied to our own pages.
What we publish. Our specification library leads with the parameters that drive selection — M/P ratio, flicker percentage, SVM, Δu′v′ — beside the standard photometric fields. Those fields are what clause 2 asks a project to demand, and they are the reason our catalogue is organised the way it is. Our science page explains the metrology behind melanopic EDI and the CIE S 026 framework, which is the background a reader needs before an eye-plane measurement means anything.
What we do not claim. No SUMLINK product is described in this article as integrative, circadian or human-centric, because the SLL's position is that no product can be. We do not claim that a specification, a luminaire or a control system improves sleep, health, alertness or performance. We hold no independent melanopic measurement report for the products in our HCL range, and none is cited anywhere in this article. What we can supply is the data a project needs to establish its own condition: the spectral fields in clause 2, the schedule and control narrative that clause 3 requires, and the measurement plan that clauses 4 and 5 turn into a handover report.
What we will not do with the 75 lx figure. We will not print it as a headline number without its version and its unit. It is a model-based reference exposure from the June 2026 version of a preprint, describing mixed light in nine sites, and it is not a measurement of any room we have supplied.
The measured daytime indoor condition is far below the consensus target: 24.0% of recorded daytime minutes reached 250 lx melanopic EDI in a nine-site study, and site-average indoor electric light measured 85.1 lx against outdoor daylight at 959.6 lx. The SLL's August 2026 position statement reads those measurements correctly and refuses the two shortcuts that would make them commercially convenient — that a short bright dose substitutes for a bright day, and that a product can be integrative in itself. What remains for a specification is narrower and more useful: name the quantity at the eye plane, demand the spectral data that converts lux into melanopic EDI, order the design daylight-first so the energy ceiling is not breached, verify the dimmed states, and receive a measurement report at handover. A room that can produce that paper has a defensible condition. A room that cannot has a claim.
Seven questions that decide whether the condition is specified or merely discussed.
Is 75 lx melanopic EDI the average for office lighting?
No, not as a measurement of an office installation. The figure is a site-average estimate for exposure attributed to indoor electric light in the 16 June 2026 version of a nine-site wearable study, where it was reported as approximately 75 lx. The same study's 23 September 2026 version reports 85.1 lx with a 95% confidence interval of 71.6 to 101.1 lx. The value describes mixed light recorded at the eye across participants' days, not the output of a luminaire or the condition of a room.
How much of the day actually meets the 250 lx melanopic EDI recommendation?
In the same study, 24.0% of recorded daytime minutes met it: 137,792 of 573,712 valid minutes. The authors state that these pooled-minute percentages describe how often exposure lay within range, not participant adherence, so the figure counts minutes rather than people. The modelled comparison by day type was 26.6% on work days and 21.5% on free days.
Does a 500 lx horizontal desk design meet the daytime melanopic condition?
It does not establish it. Melanopic EDI is assessed at the eye, on a near-vertical plane, and the conversion from the horizontal working plane depends on room geometry, surface reflectance, view direction and the spectrum of the light. Two rooms with the same desk-plane illuminance can deliver different eye-plane melanopic EDI. The condition has to be measured or modelled at the eye plane, not inferred from the desk figure.
How do I convert a vertical illuminance into melanopic EDI?
Multiply the photopic vertical illuminance by the melanopic daylight efficacy ratio of the light at that point. The ratio is a property of the spectrum, not of the fitting: the field data in this article have a median of 0.724 for the mixed light recorded. At that ratio, a 250 lx melanopic EDI condition needs about 345 lx of vertical photopic illuminance. That arithmetic is an internal estimate for illustration; the project still has to measure the plane.
Is a high CCT luminaire the same as a high melanopic output?
No. The Society of Light and Lighting states that CCT alone is insufficient and can be misleading. Melanopic efficacy is a spectral property that is not fixed by the colour temperature, so two 4000 K sources can differ in melanopic daylight efficacy ratio. Ask for the ratio from a test report, not for a colour temperature.
Can a product be described as integrative, circadian or human-centric?
The SLL's position is that no lighting product is intrinsically integrative, circadian or human-centric, because those are properties of the pattern of light exposure a product helps create rather than of the product itself. A specification can require a light condition; a product can contribute to it. A claim that assigns the property to the fitting is outside the evidence.
What should a lighting specification require so the condition can be verified?
Five things: melanopic EDI at eye level on a vertical plane across occupied hours, the melanopic efficacy of every source from a test report, a daylight-first design sequence before electric power is set, verification at the dimmed daytime and evening states, and a handover measurement report that names the instrument, its calibration date, its accuracy and the measurement positions. The last item is what makes the first four auditable.
Request BOM & Spec Sheets — the bill of materials for a project can carry the fields this article asks for: M/P ratio, flicker percentage, SVM and Δu′v′ beside the standard photometric data, with the luminaire schedule mapped to the zones that will be measured. Ask for the specification library and state which zones need an eye-plane measurement at handover: https://www.sumlink.hk/catalog