Lighting designers and obtrusive light assessment

The question of who can do a lighting assessment for planning has no statutory answer. No licence or protected title exists, so in principle anyone can write one. In practice, councils reject assessments that are not built on the Institution of Lighting Professionals guidance on obtrusive light, and environmental health officers can tell within a page whether the author has used it before. The competence that matters is the ability to model vertical illuminance at a specific window and defend the number, not a letterhead.

A lighting assessment is a report where professional input is strongly recommended rather than legally required. Councils usually expect a suitably qualified author, and professional review before submission is sensible on any scheme where residents are close or the site is dark.

What the assessment has to show

Five outputs, and a report missing any of them will come back.

The environmental zone is the decision that drives everything else, and it is the one most often got wrong. A site on the edge of a small village is not in the same zone as a town centre, and placing it in a brighter zone to make the numbers work is the error officers look for first. State the zone, the reason, and whether the authority has published its own zone mapping.

Curfew hours are set locally, commonly from 11pm, and the post-curfew limits are far tighter than the pre-curfew ones. Design for the post-curfew condition and the rest usually follows.

The guidance that sets the method

Guidance Note 1 from the Institution of Lighting Professionals, on the reduction of obtrusive light, is the document the assessment is measured against. It sets limits by environmental zone for light intrusion, luminaire intensity, upward light and building luminance, and it distinguishes pre-curfew from post-curfew. Read the current edition, because the figures and the zone descriptions have changed between versions.

Alongside it sit the standards for the specific application. Sports lighting has its own standard with class-based illuminance and uniformity requirements. Road lighting follows the relevant British Standard series and the local highway authority's own specification. Outdoor workplaces have their own standard for task illuminance.

National planning guidance on light pollution sets the policy frame: the effect on amenity, on intrinsically dark landscapes and on nature conservation. The framework edition published on 17 August 2026 carries that through into policy. Separately, artificial light emitted from premises can be a statutory nuisance under the Environmental Protection Act 1990, with a best practicable means defence for industrial, trade and business premises and a list of exempt premises including airports, harbours and prisons. That regime bites after the development is built, which is why environmental health officers take the planning stage seriously.

Membership and qualification routes in lighting

There is no single register, so look for a combination.

• Membership of the Institution of Lighting Professionals, with the Exterior Lighting Diploma being the sector's recognised technical qualification
• Membership of the Society of Light and Lighting, which sits within the Chartered Institution of Building Services Engineers, and the lighting diploma it awards
• Chartered engineer status through a relevant institution, which evidences general engineering competence rather than lighting specifically
• Documented experience of assessments against the obtrusive light guidance, on schemes of comparable type

The last of those is the most useful and the one least often asked for. A lighting designer who specifies retail interiors is not necessarily the right author for a floodlit yard next to housing. Ask for two assessments on comparable sites, and ask whether either was challenged by an environmental health officer and what happened.

Manufacturer and supplier design services are a special case. They produce competent photometric modelling, often free, and they have an interest in the specification. Use the model, have the assessment written by someone without a stake in the luminaire choice, and say in the report who produced each part. The naming point in why every planning report needs a named author and date matters here more than on most reports.

Modelling spill, glare and sky glow

The modelling is only as good as its inputs. Three of them carry most of the error.

1. Photometric files. The model must use the manufacturer's measured data for the exact luminaire, optic and output, not a generic file for the product family.
2. Mounting geometry. Height, tilt, orientation and the presence of a flat glass or shielded optic change the result far more than the lamp output does.
3. Receptor positions. Vertical illuminance has to be calculated at the actual window planes of the nearest habitable rooms, at the right height, not at a notional boundary point.

Outputs should include an isolux spill plot over a site plan with the receptor windows marked, a table of vertical illuminance at each window for both curfew conditions, intensity figures towards each receptor, and the upward light ratio. A single plan with contour lines and no tabulated numbers is not an assessment.

Boundary treatment is where a scheme is usually saved. Raising a fence, moving a column two metres, changing from a symmetric to an asymmetric optic, or adding a side shield will often bring a failing window inside the limit without reducing the lit area at all.

Ecology input where bats are present

Lighting and ecology have to be designed together, and on many sites the ecological constraint is tighter than the amenity one. Joint guidance from the Institution of Lighting Professionals and the Bat Conservation Trust sets out the approach for bats and artificial lighting at night, and it is the document ecology consultees cite.

The practical measures are consistent: keep light off roosts, access points and commuting routes, use warmer colour temperatures with reduced short-wavelength content, set luminaires to zero uplight, use tight optics and shields rather than lower output, and build in dark corridors along hedgerows and treelines. Where a roost is present, the survey and any licence work needs a suitably licensed ecologist, and the Bat Survey has to come before the lighting layout is fixed rather than after.

Designing the lighting first and asking the ecologist to approve it is the sequence that produces redesign. Give the ecologist the draft layout at concept stage.

How environmental health reviews the report

The officer checks four things, in this order. Whether the environmental zone is right. Whether the receptors chosen are the closest and most sensitive ones. Whether the post-curfew figures meet the limits. And whether the luminaire schedule in the report matches the one in the model.

That last check catches a surprising number of reports, where the model was run on one product and the schedule lists another. Where the officer's view differs from your consultant's, the disagreement is nearly always about the zone or the receptor selection rather than the arithmetic, and the approach in when the council's expert disagrees with your consultant applies.

Expect a condition requiring a detailed lighting scheme to be approved before the lighting is installed, with the luminaire schedule, photometric data, mounting details and the curfew control arrangement. Build those into the application and you avoid a second round.

Writing the lighting brief

Brief the designer in writing and keep it short. State the environmental zone you believe applies and ask them to confirm or correct it. Name the receptors, including upper floor windows and any garden amenity space. Give the curfew hours. State the ecological constraints and attach the ecology report. Set out the operational requirement, including the hours the site must be usable and any security or sports lighting class to be met. Ask for the five outputs listed above, with the model files available on request.

Then ask one more question: what would you change if the limits were not met. A designer who answers with shields, optics and geometry is thinking the right way. One who answers by moving the site into a brighter zone is not. You can find reviewers who sign off lighting work through the professional directory, and the scope of the document itself is set out on our Lighting Assessment page.

This is general guidance, not legal advice. Check the requirements with your local planning authority or a qualified lighting professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.