Designing lighting to meet dark-sky requirements
From analysis, through the design decisions, to calculated verification and the certification routes.
A working guide for the lighting designer who has been handed a requirement to limit light pollution and needs an ordered path through it, not just a table of limit values.
The limit values are published. The order of work is not.
The published guidance sets out criteria, assessment methods and tables of limits. What none of it sets out is the order to work in — which decisions to take first so they do not have to be taken twice. This manual sets that out in three parts — first the dependencies between parameters, then the path through the work, then assessment and certification.
Part two is our own sequencing of those requirements, and we call it the Lucid Dark Sky Design Workflow. It is not an industry standard and does not pretend to be one. It is the order we work in, because each step cuts down the work the next one has to do. It does not replace any procedure required by legislation, an authority, a technical standard or a certification body.
We start with the terms, because without them the rest reads as jargon.
Key terms used in this guide.
Four photometric quantities are the ones most often confused. Three of them answer three different questions: how much light there is, how much goes in a given direction, and how much lands on a surface. The rest turn up as the parts go on.
| Term | What it means |
|---|---|
| Receptor | A person, property, habitat or other element that may be affected by the installation: a resident of a neighbouring building, a user of a space, a sensitive habitat. Not a sensor and not a device. |
| Assessment location | The point, line, plane or viewing position at which a criterion is calculated or measured — the plane of a window, a defined observer position, a surface required by the method. A site boundary may be an assessment line, but it is not a receptor. |
| Environmental zone | Within the CIE 150 framework, sites are classified E0 to E4 by the character of their surroundings. The classification determines a number of the recommended obtrusive-light limits and therefore has an important influence on the design. It should only be used where that framework forms part of the applicable assessment. |
| Light pollution | The everyday term. In the standards it resolves into measurable components, referred to collectively as obtrusive light — and it is those components that carry parameters. |
| Sky glow | The brightening of the sky above a lit area. A combined effect of many installations at once rather than of any single one. |
| Luminous flux | The total amount of light a luminaire puts out, in lumens. It answers: how much light is there at all. |
| Luminous intensity | The amount of light in one particular direction, in candelas. It answers: how much light goes that way. Luminous intensity toward an observer is one of the parameters used to assess the impact of bright luminaires in the field of view. |
| Illuminance | The amount of light arriving at a surface, in lux. It answers: how much light lands here. Vertical illuminance is measured on a vertical plane — a window pane, for instance. |
| Luminance | How bright a surface looks to the eye, in candelas per square metre. For facades and signs the limit is set on this rather than on illuminance. |
| Upward light ratio (ULR) | What share of a luminaire’s flux goes out above the horizontal, as a percentage. In the darkest zones it has to be zero. |
| Upward flux ratio (UFR) | Applies to a whole installation and can cover both the direct and the reflected upward component. It is not required on every scheme — current guidance applies it in defined types of installation and location rather than universally. |
| Curfew | The time after which more restrictive requirements apply or the installation changes its operating condition. Curfew does not mean midnight — its timing follows from the requirement applicable to the project. |
| Baseline | The documented existing condition needed to evaluate the impact of a proposed installation. Its scope depends on the criterion being assessed and usually covers existing lighting and its effects. A night-sky-quality survey is a different kind of data, undertaken where a particular procedure or programme calls for it. |
| Criteria sheet | A standalone document of target values, issued before concept design. Compliance is reported against it at every later stage. |
| Calculation scene | A separate set of surfaces and settings within the model, serving one specific assessment. The design scene and the obtrusive light scene are two different scenes. |
| Projected area | How large a luminaire appears from wherever it is being looked at. It changes with the observer’s position, even for identical fittings. |
What depends on what.
The requirements arrive as numbers, and those numbers are not independent of each other. Before anything gets drawn, it is worth knowing which way those dependencies run.
The zone sets the limits, the limits set the concept
The environmental zone classification is the governing variable. Every permitted value follows from it: the share of flux above the horizontal, illuminance at receptors, luminous intensity, surface luminance. Only then does the concept follow — spacing, mounting heights, optics. The dependency runs one way, and working against it ends in a redesign.
Three phenomena, three different quantities
Obtrusive light is not one thing. Bright luminaires in the field of view are assessed as luminous intensity toward the observer, light reaching neighbouring premises as vertical illuminance at the window, and the contribution to sky glow as the share of flux sent into the upper hemisphere. Improving one does not improve the others and can make them worse. There is no general rule that lowering a luminaire reduces the light leaving a site — lower mounting often forces less favourable beam angles and more lighting points, which can increase both spill and glare. Geometry is analysed as an arrangement, not as a set of independent settings.
Direct emission is not the whole story
The per-luminaire figure covers only the flux leaving the fitting upward — CIE 150 says so at the table itself. Light reflected off paving, planting and water is additional and also reaches the atmosphere. The closer direct emission gets to zero, the larger the reflected share becomes. Which means swapping fittings for shielded ones does not close the question, not if the light level on horizontal surfaces stays where it was.
The answer depends on the hour
Where a curfew applies, assessment systems publish separate values for before and after that hour, and both are verified. A scheme then has at least two states. In the darkest zones some limits fall to zero after the curfew, which means facade and sign lighting is expected to go off rather than dim. Where the use of a place changes through the night, more than two states may be needed.
Spectrum and unbroken darkness pull in a different direction
Quantity and direction are not the whole of it. Spectral content is one of the factors affecting both scattering in the atmosphere and the response of nocturnal species — alongside light level, direction of emission and operating hours. The continuity of unlit ground can matter just as much, because it determines whether wildlife keeps its commuting routes and foraging habitat. These are requirements that change the arrangement of a scheme, not just the choice of its parts.
Lucid Dark Sky Design Workflow.
Nine steps from establishing the requirement to writing the specification. The order is not arbitrary. Skip an early step and it comes back at verification, which is where a fix costs most. The first six steps are analysis, the last three are implementation.
Establish what actually applies
Identify the binding document — national or regional law, a planning condition, authority guidance, or a design manual issued for a masterplan. Check whether the client intends to pursue certification, because that changes the scope of work rather than only the target values. Where a local code applies, it takes precedence over any international standard. In some jurisdictions — in the United Kingdom, for example — artificial light from defined premises can be treated as a statutory nuisance, with a duty on the authority to investigate complaints.
Classify the environmental zone
Propose a zone and justify it against the reference system in use. Near the boundary between two zones the stricter one applies, and the darkest zone requires a surrounding buffer that is itself a design constraint. The classification is agreed with the authority rather than assumed. This is the most consequential decision in the process and it is usually taken in the first weeks, often without the lighting designer in the room.
Establish the baseline: sky and existing lighting
Document night sky quality before work starts, by measurement or from light pollution mapping. This becomes the reference for every later assessment and, on certification routes, the baseline for periodic review. In parallel, survey the lighting already present on and around the site: limits apply to the combined effect of every installation visible from a given receptor, not to yours alone.
Identify receptors and their sensitivity
Fix the points where nuisance will be judged: windows of nearby properties at their real height, site boundaries, viewing positions. Impact assessment practice ties receptor sensitivity to the zone — highest in the darkest areas, lowest in urban ones — and then sets it against the magnitude of change from the baseline. A receptor is not equally sensitive by day and after dark.
Habitat and dark corridors
Agree sensitive areas and the commuting and foraging routes of nocturnal species with the ecologist; guidance developed with bat conservation specialists sets out a mitigation hierarchy for exactly this situation. This step comes before the layout is drawn, because its outcome governs where luminaires go, not which ones.
Close the analysis with a criteria sheet
Issue a standalone document with the target values: task illuminances by surface type, receptor limits, permitted upward flux, the assumed curfew hour, and the areas that are to stay unlit. Spectral or colour temperature criteria are included where they follow from ecological requirements, a certification programme, the client brief or local regulation — CIE 150 does not set a universal limit for them. The criteria sheet is what compliance is reported against at every subsequent issue of the documentation.
Take the design decisions in order
Quantity of light and unlit areas first. Then glare control through optics — beam angle, shielding, cowls, louvres; for area lighting, asymmetric optics set so the front glazing stays close to parallel with the lit surface are generally preferred. Then elimination of emission above the horizontal, then control at the site boundary, and finally on the vertical planes of receptors. Each step reduces the work the next one has to do.
Write the control programme as part of the design
Set out the curfew hour, dimming levels, control groups and the trigger for each change of state as a table the contractor can commission against. Control delivers most of the reduction after midnight, and its extent has to be settled at concept stage: adding addressability later usually means changing luminaires. Some assessment systems require every fitting to carry a switch-off time, delivered by time clock, occupancy sensor or local control.
Write a specification that survives product substitution
State the requirements so an approved equal cannot break compliance: backlight, uplight and glare classification, where the criteria sheet sets one, a colour temperature ceiling expressed as a requirement rather than a product name, and intensity limits in the critical directions. Ask for photometry across the full angular range — without it part of the limits cannot be verified, and the omission is usually discovered at submittal review, when correcting it is most expensive.
Calculated verification and the certification routes.
Compliance is demonstrated rather than declared. Below are the verification methods, and under them the certification routes with what each one asks of the design.
A separate calculation scene
Compliance is calculated in the same model as the design but in a scene dedicated to obtrusive light. The design scene answers whether the lighting performs its function. The obtrusive light scene answers what effect it has beyond the area and the hours it was designed for. They use different surfaces, different quantities and different acceptance criteria, so they are never the same calculation.
Surfaces where the exceedances actually occur
Calculation surfaces belong on the site boundary, at the assessment distance beyond it, and on the glazing of the nearest properties at their real height. A surface placed where it is convenient rather than where the receptor is produces a result that will not survive review.
Two time states in one document
Report evening operation and the state after the curfew hour. A document showing only one of them has not been verified. For each criterion the permitted value is set against the calculated value, per limit and per zone.
Intensity assessment is often manual work
The intensity limit depends on the observer distance and on the apparent projected area of the luminaire, which changes with viewing position even for identical fittings. The procedure is documented: find the closest realistic maintained observer position, because it is the most onerous, then determine the luminaire group by projected area. The extent of automation depends on the software: tools built to CIE 150 may perform this assessment directly, while other workflows require the calculated values to be compared against the limit by hand. Worth establishing before the fee is agreed.
Design to a margin, not to the line
A scheme that lands just under the limit will not survive construction. Fittings get aimed by hand, products get substituted, and planting grows or does not. The margin is what keeps it compliant after everything that usually happens has happened.
Checking what actually got built
Reviewing submittals against the agreed criteria, aiming and focusing on site at night, and issuing an as-installed compliance statement are what close the loop. Skip them and the documentation describes an installation nobody has ever put side by side with the real thing.
| Programme | Scope | Nature of the requirements |
|---|---|---|
| DarkSky Approved Luminaires | an individual luminaire | a product programme with its own technical criteria; in practice it acts as a filter at product shortlist stage |
| DarkSky Approved Lodging and Resorts | overnight accommodation and larger hospitality developments | sky quality, habitat identification, lighting design, and education and outreach |
| International Dark Sky Places | Parks, Reserves, Sanctuaries, Communities, Urban Night Sky Places | each category carries its own requirements and its own ongoing reporting obligations |
| Building rating systems | a credit within a wider building assessment | treated separately and always checked against the current version of the individual scheme |
There is no single generic “dark-sky certification” and no universal package of surveys, inventories and management plans that fits every route. Each programme has its own scope, its own criteria and its own way of maintaining the status, so once certification is decided the criteria of that specific programme in its current edition are what matter.
What this rests on. Parts one and three draw on sector documents: the CIE guide on limiting obtrusive light together with the national guidance that reproduces its tables, environmental lighting impact assessment practice, the guidance on lighting and bats, the five principles for responsible outdoor lighting, and the requirements of the certification programmes and building rating credits. Part two is our ordering of those requirements into a design sequence.
Where the tables stop. Technical limits do not replace ecological assessment. On sensitive sites the local code, the environmental conditions and the agreements reached with specialists and authorities take precedence.
Before you start.
Where do I start if the requirement appeared mid-project?
At step one: establishing which document is binding on this site and which framework the scheme will be assessed against. Zone classification, assessment locations, baseline conditions and limits follow from that, and only then can the current concept be tested.
Is specifying fully shielded luminaires enough?
No. That addresses direct emission above the horizontal, which is part of one of the three phenomena. Glare at angles below the cut-off, light leaving the site, and the component reflected off pale paving are all untouched by it.
Will the software calculate all of it?
Not necessarily. Some parameters are calculated directly, but the extent depends on the software and the assessment method. The intensity assessment depends on observer distance and the apparent projected area of the luminaire; CIE 150-compliant tools may handle it, while other workflows require manual comparison against the limit.
Is there a common set of documents for all certifications?
Each programme has its own scope and its own requirements, so there is no universal package. Some do, however, call for data that cannot be reconstructed afterwards — the condition before the works, for instance. Where certification is under consideration, check the criteria of that specific programme at the outset rather than after the installation is complete.
Content reviewed: August 2026. Checked against CIE 150:2017, the CIE position statement CIE PS 003:2025 on obtrusive light and light pollution, current ILP guidance, and the current criteria of the DarkSky International programmes.
Three dark sky materials. Where to start explains how the field is put together. This page is the design manual. The handbook carries the regulatory maps and a worked example.