Where to start on a project with dark-sky requirements
Do not start with the luminaire. Start by establishing what the requirement means for this particular project, which criteria apply and how compliance will be assessed.
“Dark-sky compliant” can mean several different things.
It sounds like a single technical condition. On one project the governing document will be local legislation or a planning condition. On another the client refers to CIE guidance, to a national document derived from it, or to a masterplan lighting standard. Ecological constraints may apply independently, and a certification programme may add another set of criteria.
Dark-sky design is therefore not compliance with one universal table of limits. CIE 150 provides international guidance for limiting the effects of obtrusive light; it is not a code that governs every project everywhere.
Requirements that can apply to a single project.
Projects rarely become difficult because a table of limits is missing. They become difficult when requirements from different systems arrive in one brief and are treated as though they were one set of rules. Separating them early is the useful first move.
Regulation, planning conditions and client requirements
National or regional legislation, planning conditions, authority guidance, a client standard or a design manual issued for a masterplan. This layer decides what is mandatory and what is a voluntary project objective.
Technical criteria for limiting obtrusive light
The assessment framework and reference values, most often CIE 150 or national guidance derived from it. Environmental zones, limits at neighbouring windows and restrictions on upward emission belong here — but only where that framework has actually been adopted for the project.
Ecological and environmental requirements
Habitats, sensitive species, movement routes. CIE states plainly that standard lighting metrics are built on human vision and are not meaningful for ecological assessments, so this layer cannot be reduced to a single colour temperature or a single illuminance limit.
Certification or dark-sky programme
Where a client is pursuing a particular status, that programme’s criteria form a separate layer. They are not interchangeable with CIE, with national guidance or with local planning requirements, and they need checking against the current version of that specific programme.
Not “which luminaire”, but “what will this be assessed against”.
Only once the governing document is established is it possible to say which parameters have to be checked and which deliverables will be needed.
Where CIE 150 or CIE-based guidance applies, one of the first determinations is the environmental zone, E0 to E4. It describes the character of the surroundings and is used to set some of the recommended limits. It is not a universal zoning system that can be imposed on any project: identify the governing framework first, classify the site within it second.
A receptor is not an assessment location.
A receptor is 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. It is not a sensor or a device.
An assessment location is 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 applicable method.
The distinction has practical consequences. A site boundary may well be an assessment line where a method requires it, but nobody lives on a boundary, so it is not in itself a receptor. Conflating the two tends to produce calculation planes placed where they are convenient to model rather than where the criterion actually applies.
A baseline is not automatically a night-sky measurement.
For an obtrusive-light assessment the baseline is usually the existing lighting condition against which the effect of the proposed scheme is judged. Limits generally apply to the combined effect of everything visible from a given location, not to the proposed installation in isolation.
A night-sky-quality survey is a different kind of data. It may be required by a particular certification programme or site designation, but it is not a universal first step.
Meeting the technical limits does not make a scheme ecologically neutral.
In its 2025 position statement CIE says plainly that standard lighting metrics are based on human visual perception and are not meaningful for ecological assessments, because most species respond to light differently from people.
One finding is worth stating because it contradicts a common assumption: warm light is not inherently safe. Bats, fireflies, freshwater fish and passerine birds are among the species whose photoreceptor sensitivity extends past the blue end into longer wavelengths. CIE recommends tailoring solutions to the species actually present and treats spectral tuning as one tool among several rather than as a complete answer.
In some locations the appropriate response is to reduce the light level, shorten the operating period, move the luminaires, or leave an area unlit.
The criteria sheet closes the analysis.
Once the governing requirements, assessment framework, relevant locations, baseline conditions and ecological constraints are understood, they can be consolidated into one document. It should carry only the criteria that actually apply, and each one should name its source — legislation, technical guidance, ecological advice, certification or the client brief.
The lighting layout and the luminaire selection follow those decisions rather than preceding them.
Questions that follow straight after.
Does dark-sky design simply mean using less light?
No. CIE explicitly recognises the benefits of light at night — lower collision risk, reassurance when moving through a space, less isolation for older people and for women after dark — and supports mitigating the unwanted effects rather than pursuing darkness. It is also worth noting that a well-designed, uniform scheme often achieves its purpose at a lower average level, because the eye is not readapting between bright and dark patches.
The requirement appeared halfway through design. Where do I start?
With the source of the requirement and the framework the scheme will be assessed against. Classification, assessment locations, baseline conditions and limits follow from that, and only then can the current design be tested against them.
Is a night-sky-quality survey always required?
No. It should be undertaken where a particular programme or assessment method calls for it. It is not a universal requirement of every CIE-based assessment.
Are fully shielded luminaires enough?
No. They address direct upward emission, but not reflected upward light, intrusion into neighbouring premises, bright sources in the field of view, excessive facade luminance or ecological effects.
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.