Lighting assessment costs and the modelling behind them
Lighting assessment fees are driven by the number of windows modelled, whether a night survey is needed, and how often the layout changes after the model is built.
The lighting assessment cost planning applications attract is driven by three things: how many neighbouring windows have to be modelled, whether a night-time baseline survey is needed, and how many times the layout changes after the first model is built. The modelling itself is quick once the inputs exist. Assembling the inputs is where the hours go, and reruns after a layout change are charged again because the calculation has to be rebuilt.
Fix the car park layout before you commission the lighting report. That single decision saves more than any negotiation on the fee.
Environmental zone and the limits that apply
Obtrusive light in England is assessed against the Institution of Lighting Professionals guidance on reducing obtrusive light, which divides the country into environmental zones from the darkest to the brightest. The zone determines the limits that apply, and the limits differ before and after a curfew time, typically late evening.
| Zone | Character | Effect on the assessment |
|---|---|---|
| E0 | Protected dark skies | The most demanding limits, with very little tolerance for upward light |
| E1 | Intrinsically dark, such as National Parks and National Landscapes | Strict limits, and often a requirement for no lighting at all in some areas |
| E2 | Low district brightness, rural and village | Moderate limits, with a meaningful difference after curfew |
| E3 | Medium district brightness, suburban and small town centres | The most common zone for commercial schemes |
| E4 | High district brightness, busy town and city centres | The most permissive limits |
The guidance sets values for sky glow, for light trespassing into windows measured as vertical illuminance, for luminaire intensity towards a receptor, and for the luminance of an illuminated building face. Take the current numbers from the current edition rather than from an older report, because they have been revised.
Disputes about the zone are common and they matter financially, because an E2 assessment on a site the authority thinks is E1 will be rejected and rerun. Agree the zone with the environmental health officer in writing before the modelling starts. Where the site adjoins a dark area, expect to assess against the stricter zone at the boundary even if the site itself sits in a brighter one.
Baseline measurement where needed
Not every assessment needs a night-time survey. Where it does, it adds a visit, travel, out-of-hours time and a return visit if the weather fails.
A baseline is usually needed when the authority disputes the environmental zone, when an existing lighting installation is being replaced and the comparison matters, when a complaint has already been made, or when the receptor is in a location where the existing condition is uncertain. It is usually not needed on a greenfield site in an obviously rural setting, where the zone can be established from the designations and the context.
The survey itself is a set of calibrated illuminance readings at the receptor positions, taken with the subject lighting off where that is possible, in dry conditions away from a full moon, and outside the hours when passing traffic dominates. Access to a neighbour's garden or a first floor window is the usual obstacle, and the honest answer is often a reading from the nearest publicly accessible point with the limitation recorded. That is the same discipline as any environmental survey, and it is priced the same way as the monitoring period in a noise brief, as the note on budgeting a noise survey sets out.
Modelling vertical illuminance at receptors
The core calculation places a vertical plane at each sensitive window and computes the illuminance on it from every luminaire in the scheme. The cost scales with the number of receptors and with the complexity of the geometry between the lights and the windows.
What drives the hours up:
- A long boundary with many dwellings, each needing its own calculation plane at ground and first floor level.
- Sloping ground, which means the calculation grid cannot be built from a flat plane and levels have to be modelled.
- Screening by buildings, fences and vegetation, which has to be modelled as geometry if you want credit for it, and ignored if you do not.
- Several luminaire types on different mounting heights and tilts.
- A requirement to assess glare as well as illuminance, which is a separate calculation.
- Reflected light from large glazed or pale facades, which some authorities ask about.
Screening is where applicants lose money without realising. Claiming the benefit of a 1.8 m fence requires it to be in the model, dimensioned, and secured by condition so it cannot be removed. Claiming the benefit of a hedge is harder, because a hedge is deciduous or it is not, and in winter it is not.
A Lighting Assessment reporting against the guidance should present the modelled values at each receptor against the pre-curfew and post-curfew limits for the agreed zone, with the calculation assumptions stated. Councils usually expect a suitably qualified author for this work and professional review is strongly advised.
Luminaire data and photometric files
The model needs a photometric file for every luminaire type, supplied by the manufacturer in a standard format. No file, no calculation.
This is a frequent cause of delay. A design that specifies a luminaire by a trade description rather than a catalogue number cannot be modelled. A design that changes the luminaire after the model is built needs the calculation rerun. And a luminaire chosen for its appearance rather than its optical control, such as a decorative lantern with an exposed lamp, will fail the upward light limits in a dark zone no matter how the rest of the scheme is designed.
Specify by catalogue number, with the photometric file, the lumen output, the colour temperature and the proposed dimming or switching regime. Warmer colour temperatures matter for ecology as well as amenity, and most authorities now expect a limit on correlated colour temperature near habitat. Where bats are present, the joint lighting and bat conservation guidance applies, and the lux levels along commuting corridors become a design constraint rather than an amenity one. A Preliminary Ecological Appraisal will identify whether that is in play, and councils expect a suitably qualified author for ecological work with professional review strongly advised.
Reruns after a layout change
The single largest avoidable cost. A lighting model is built on a fixed geometry: column positions, mounting heights, building footprints, levels and boundary treatments. Change any of those and the model is rebuilt rather than adjusted.
The changes that trigger a full rerun: moving the building, changing the car park layout, changing column positions or heights, changing the luminaire, changing the boundary treatment, and changing the levels. The changes that usually do not: adjusting the switching regime, reducing the output of an existing luminaire type by dimming, and adding a shield to a specific luminaire.
Sequence the work accordingly. Settle the layout, the levels and the boundary treatment first. Then commission the lighting design. Then model it. Clients who commission the lighting assessment at the same time as the architect starts the layout pay for the same report two or three times.
Where a rerun happens because the authority asked for a change, that is a legitimate extra. Where it happens because the layout was not fixed, it is money burnt.
Commissioning measurements after installation
Expect a condition requiring post-installation verification. It usually asks for measured illuminance at the receptors, confirmation that the luminaires are installed at the modelled heights and tilts, and confirmation that the switching or dimming regime is set as approved.
That is a further visit, out of hours, with a short report. Budget for it at the outset rather than discovering it after practical completion, because at that point the contractor has left and any correction is a separate mobilisation.
Two things reduce the risk of failing verification. Aiming angles and tilts specified on the installation drawing rather than left to the electrician, because a luminaire tilted 10 degrees more than modelled changes everything. And a commissioning record signed by the installer, which turns an argument into a document. Where the condition is a pre-occupation requirement you cannot satisfy on time, the consequences are the same as any condition you cannot discharge, as the note on a pre-commencement condition you cannot discharge describes.
Scoping to control the fee
Six steps, in order, that keep the cost proportionate.
- Agree the environmental zone with the environmental health officer in writing, and agree the receptor list at the same time.
- Ask whether a baseline survey is required, and if the officer says yes, ask what it is for.
- Fix the site layout, levels, column positions and boundary treatment before instructing.
- Specify luminaires by catalogue number with photometric files attached to the brief.
- Ask the consultant to quote the base assessment and the price per rerun separately, so a change is a known cost rather than a surprise.
- Include the post-installation verification visit in the original appointment.
One honest uncertainty. Authorities differ in how strictly they apply the boundary between zones and in whether they will accept screening by planting, and there is no national arbiter on either. Asking the question at pre-application stage is the only way to find out what your authority does.
For what PlanScope charges to draft the supporting documents around a lighting scheme, see pricing.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
Frequently asked questions
What determines the limits in a lighting assessment?
The environmental zone, which runs from protected dark skies through intrinsically dark areas such as National Parks to high brightness city centres. The guidance sets values for sky glow, light into windows, luminaire intensity and building luminance, with different figures before and after a curfew time. Agree the zone with the environmental health officer before modelling.
Is a night-time baseline survey always needed?
No. It is usually needed where the environmental zone is disputed, where an existing installation is being replaced and the comparison matters, where a complaint has already been made, or where the existing condition at a receptor is uncertain. On an obviously rural greenfield site the zone can normally be established from designations and context.
Why do lighting consultants charge again for a rerun?
Because the model is built on fixed geometry. Moving the building, changing the car park layout, altering column positions or heights, swapping the luminaire or changing the boundary treatment means the calculation is rebuilt rather than adjusted. Adjusting the switching regime or dimming an existing type is usually a smaller change.
Can I claim credit for a fence or hedge as screening?
A fence can be modelled as geometry, dimensioned and secured by condition so it cannot be removed, and the benefit is then real. A hedge is harder, because a deciduous hedge provides little screening in winter and authorities are reluctant to rely on planting that can be cut back or die.
Will the council require measurements after installation?
Commonly yes, by condition. The verification usually covers measured illuminance at receptors, confirmation that luminaires are at the modelled heights and tilts, and confirmation of the switching regime. Specify aiming angles on the installation drawing and obtain a signed commissioning record, because corrections after the contractor leaves are expensive.
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.