Budgeting a lighting assessment to ILP GN01
Lighting assessment fees are driven by the environmental zone, whether a baseline night survey is needed and how many design iterations the officer asks for. Budget it as a design service, not a document.
The cost of a lighting assessment is driven by three things: whether a baseline night-time survey is needed, how many luminaires end up in the model, and how many rounds of redesign the environmental health officer asks for. Lighting work for a car park, a drive-through, a sports pitch or a yard is rarely a single fixed deliverable, so budget it as a design service with a report attached rather than as a one-off document.
Obtrusive light assessment work follows the Institution of Lighting Professionals guidance note on the reduction of obtrusive light, usually shortened to GN01. The guidance sets the parameters an officer will test your scheme against, which means the parameters also set the scope of work you are paying for.
What the assessment actually covers
An obtrusive light assessment is a calculation exercise with a written interpretation. The lighting designer builds a model of the site, the luminaires, their mounting heights, aiming angles and optical control, then predicts what that installation does to the surroundings at night.
Four effects are examined. Light trespass into neighbouring windows, measured as vertical illuminance at the window plane. Glare from the luminaire itself, expressed as luminous intensity in a direction towards a receptor. Sky glow from light emitted above the horizontal. And the luminance of any illuminated building or sign surface.
The report then compares predicted values against the limits for your environmental zone, identifies where the design fails, and proposes changes. Lighting assessments sit in the group of report types where councils usually expect a suitably qualified author and professional review is strongly advised, because the output is a set of engineering calculations rather than a narrative.
Environmental zones and why they change the fee
GN01 divides the country into environmental zones, from intrinsically dark areas through rural and suburban settings to brightly lit town and city centres. Each zone has its own numerical limits, and the limits tighten sharply as the zone gets darker. The same car park lighting scheme can pass in a city centre and fail by a wide margin in a village.
Nobody publishes a map of these zones. The lighting designer assigns one from the local plan designation, the surrounding land use and the existing lighting environment, and the officer may disagree. That disagreement is where unbudgeted hours go, so ask your consultant to confirm the proposed zone with the authority in writing before the detailed modelling starts.
| Setting | Typical zone character | Effect on cost |
|---|---|---|
| National Park, dark sky area | Intrinsically dark | Highest, often requires a completely different scheme |
| Open countryside, isolated farm | Dark rural | High, usually needs a baseline survey |
| Village, rural fringe | Low district brightness | Moderate, several design iterations likely |
| Suburban, small town | Medium district brightness | Standard scope |
| Town or city centre | High district brightness | Lowest, limits rarely binding |
Baseline measurement and when it earns its cost
A baseline survey means someone standing on site after dark with calibrated equipment, recording existing illuminance at the positions where receptors are. It costs a site visit, travel and a return journey if the weather is wrong.
It is worth paying for in two situations. Where the environmental zone is contested, measured existing conditions are the strongest evidence for arguing a less restrictive zone. And where there is an existing lit use being replaced, the comparison between before and after is often the whole case. On a suburban infill plot next to street lighting, a baseline adds little that the model cannot show.
Modelling, iterations and the part people underestimate
The modelling itself is quick once the inputs are fixed. The inputs are the problem. Luminaire selection, column heights, the exact positions after the drainage layout moves, the boundary treatment that may or may not survive the tree officer's comments, and the operational hours the client has not yet decided.
Each change means re-running the calculation and re-issuing the drawings and tables. Two or three iterations before submission is normal. A further round after consultee comments is common, and if the environmental health officer asks for a different zone, the whole model may need rebuilding against tighter limits.
Price this as a schedule rather than a lump sum. Ask for the fee broken down into the base model, each additional iteration, the report, and any post-determination work. That way a change to the car park layout produces a known cost rather than an argument. The same logic applies to the other technical disciplines, which is why it helps to know what a planning agent's fixed fee usually includes before you assume the lighting work is inside it.
Spill, glare and upward light in practice
Three design moves do most of the work, and they have very different cost implications.
- Reducing mounting height and increasing the number of columns lowers spill and glare, but adds capital cost and more luminaires to model.
- Flat-glass luminaires with sharp cut-off optics control upward light almost completely, and cost more per unit than the alternatives.
- Rotating the aiming angle away from a boundary is free in the model and often impossible on site once the parking bay layout is fixed.
Floodlighting is the expensive case. A pitch or a yard needs a given illuminance on the working plane, and achieving that while keeping intensity towards nearby windows within limits usually means more columns, tighter optics and sometimes external louvres. If the site is in a dark zone and the neighbours are close, there may be no design that passes, and the honest answer at feasibility stage saves a wasted application.
Curfew hours and the conditions that follow
GN01 applies different limits before and after a curfew, commonly set at 23:00 and confirmed by the local authority. After curfew the permitted values drop sharply, and in the darkest zones they approach zero.
That matters commercially. A gym open until 22:00 is assessed against pre-curfew limits for its whole operating period. The same gym open until midnight has to meet post-curfew values for the last hour, which may mean a separate low-level scheme, part-night switching, or dimming controls. The assessment has to model both states, which is more work than modelling one.
Expect conditions requiring the installation to be built as approved, a lighting control strategy, part-night dimming or switch-off times, and sometimes a prohibition on additional lighting without further consent. Read those carefully against the business plan. Changing them later means a section 73 application and another round of assessment.
Post-installation verification
Many authorities now condition a verification exercise: after the lights are installed and commissioned, a competent person measures actual illuminance at the receptor positions and reports whether the approved limits are met. It is a separate visit, a separate report, and in most cases a separate fee that was never in the original quotation.
Budget for it at the start. Where verification finds an exceedance, the remedial work is re-aiming, shielding or replacement, and the cost of that falls on whoever installed the scheme. Specifying the approved luminaire rather than an equivalent is the least costly insurance available.
A Lighting Assessment draft gives you the policy framework, the structure the officer expects and the right set of questions to put to the lighting designer, which shortens the specialist's input to the calculation work itself. That is the same split that works for ground investigation, where the reporting structure is predictable and the site investigation budget goes on fieldwork.
PlanScope's own prices are published and fixed: one free report, £50 per report, or £150 per month for unlimited reports on the Professional tier, with the annual option at £600. Consultant fees for lighting design are not published anywhere reliable and vary with the number of luminaires and the zone, so get two quotations against a written scope rather than working from a figure you read somewhere. See PlanScope pricing for the report side of the budget.
This is general guidance, not legal advice, and lighting requirements are set by your local planning authority, so confirm the environmental zone and any verification requirement with them before you commission work. For specialist technical reports, qualified professional input may be required. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
What is ILP GN01?
It is the Institution of Lighting Professionals guidance note on the reduction of obtrusive light. It sets limits for light trespass into windows, luminaire glare, upward light and building luminance, with different values for each environmental zone and separate limits before and after a curfew. Local planning authorities use it as the assessment framework for external lighting.
Which environmental zone applies to my site?
There is no published map. The lighting designer assigns a zone from the local plan designation, the surrounding land use and the existing lighting environment, and the local authority may take a different view. Agree the zone in writing with the authority before detailed modelling starts, because a change of zone can mean rebuilding the model against tighter limits.
Do I need a night-time baseline survey?
Not always. It earns its cost where the environmental zone is contested, because measured existing conditions are the strongest evidence, and where an existing lit use is being replaced and the comparison matters. On a suburban plot already lit by street lighting, the calculation model usually tells the officer everything needed.
What is a lighting curfew in planning terms?
GN01 applies tighter limits after a curfew time, commonly 23:00 and confirmed by the local authority. Operating beyond that hour means the scheme has to meet much lower values, which usually requires part-night dimming, switching or a separate low-level installation. Both states have to be modelled, so late opening increases the assessment scope.
Is post-installation verification usually conditioned?
Many authorities now require it. A competent person measures actual illuminance at receptor positions after commissioning and reports whether approved limits are met. It is a separate site visit and report, often omitted from the original quotation. Installing the approved luminaire rather than a substitute is the simplest way to avoid remedial work.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.