Lighting assessment or an obtrusive light report
One document proves the lighting works, the other proves it does not harm the neighbours or the bats. Here is the difference, how ILP environmental zones are argued, and what to submit for a small scheme.
Asked for a lighting assessment or obtrusive light report, most case officers mean the second and most lighting designers quote for the first. A lighting assessment is a design document: it works out what illuminance a space needs, selects luminaires and proves the scheme meets the relevant standard. An obtrusive light report is an impact document: it takes a lighting design, applies the Institution of Lighting Professionals environmental zone limits and reports whether sky glow, light intrusion and luminaire intensity stay inside them. They overlap, they are costed differently, and submitting the wrong one is the commonest reason a lighting condition cannot be discharged first time.
What a lighting assessment contains
A lighting design assessment answers the question "does this scheme light the space properly". For an external scheme it usually contains a description of the task areas and their required maintained illuminance, the design standard applied, a luminaire schedule with photometric data files, mounting heights and tilt angles, a maintenance factor, and calculation grids showing average and minimum illuminance plus uniformity.
The standard depends on what is being lit. Adopted roads follow BS 5489-1, outdoor work places follow BS EN 12464-2, sports pitches follow the relevant governing body guidance, and a car park or forecourt is usually designed to the client's own insurer-driven brief. None of those standards concerns itself with the neighbours. That is the gap the second document fills.
Environmental zones and the measures that go with them
The ILP's guidance on the reduction of obtrusive light, GN01, classifies the receiving environment into zones from E0, an intrinsically dark area such as a National Park or a dark sky reserve, through E1 for a dark rural area, E2 for a low district brightness area such as a village or rural industrial estate, E3 for a suburban or medium brightness area, up to E4 for a high brightness urban centre.
But the zone has to be argued rather than asserted. Councils in rural districts will treat a village edge as E2 where an applicant has assumed E3, and the difference in permitted light intrusion between the two is large. Set the zone in the scoping stage with the environmental health or planning officer and record who agreed it.
Four measures are then reported against the zone limits:
- Sky glow, expressed as the upward light ratio of the installation, which is the proportion of flux emitted above the horizontal.
- Light intrusion into windows of relevant properties, expressed as vertical illuminance in lux at the plane of the window.
- Luminaire intensity towards an observer at a relevant window, in candelas.
- Building or structure luminance, in candelas per square metre, where a facade or sign is lit.
Each measure has a pre-curfew and a post-curfew value, with the post-curfew figures much tighter. The curfew time is set locally and 23:00 is common, so confirm it from the council's own supplementary guidance rather than defaulting to it. Take the numerical limits from the current edition of GN01 itself, because they have been revised and quoting an old table is the fastest way to lose credibility with a reviewer.
Obtrusive light as a separate question
An obtrusive light report exists to answer a planning objection. Its structure follows the receptors rather than the design.
Identify every relevant property and window within the zone of influence, with window heights and orientations from a measured survey or photographs rather than assumption. Model the vertical illuminance at each of those windows and the luminaire intensity in the direction of each. Report the results against the zone limits in a table that names the window, not just a grid reference. Then deal with anything that exceeds a limit by changing the design: lower mounting height, a flat glass optic rather than a bowl, zero uplight, a louvre or cowl, a redistributed beam, or part-night switching.
Artificial light can also be a statutory nuisance under section 79 of the Environmental Protection Act 1990, with exemptions for certain premises including outdoor relevant sports facilities. That matters to the drafting: a scheme that satisfies GN01 is not automatically immune from a nuisance complaint, and the report should not imply otherwise. For the restaurant and takeaway cases where lighting arrives alongside plant noise and extraction, the sequencing described for a noise or odour assessment applies to lighting too.
Lighting and ecology
Ecological lighting is a third discipline again, and it is not covered by GN01's zone limits. The reference point is the joint ILP and Bat Conservation Trust guidance on bats and artificial lighting, which deals with spectrum, timing, direction and the lux levels on commuting and foraging routes rather than with amenity.
What a reviewer looks for: a correlated colour temperature at the warm end, usually 2700 K or lower, with the blue content minimised. No upward light and no light on hedgerows, treelines, watercourses or roof voids used by bats. Mounting heights and shields that keep spill off the dark corridor rather than merely off the neighbour's window. Part-night or dimming regimes tied to the species present. Where a bat survey has identified a roost or a commuting route, the lighting design has to be checked by the ecologist before it is submitted, and surveys plus any licence require a suitably licensed ecologist under the Wildlife and Countryside Act 1981 and the Conservation of Habitats and Species Regulations 2017.
And the conflict between amenity and ecology is real. Reducing spill towards housing by tilting a luminaire can push light onto a hedgerow. Say which constraint governed the final design.
Outputs a case officer can actually read
Officers are not lighting engineers. Three outputs do most of the work.
A plan with isolux contours at ground level, drawn at the contour values that matter locally rather than the software default, with the site boundary and the nearest windows shown. A table of results by receptor, with the limit alongside the predicted value and a pass or fail column. And a short luminaire schedule with the make, model, output, optic, mounting height, tilt and any accessory, because that is what a condition will be drafted against.
What slows a determination down: calculation grids with no boundary shown, results quoted as averages across a site when the limit applies at a specific window, photometric files that do not match the luminaires in the schedule, and an assessment that models the design intent while the contractor installs something else.
Conditions and the post-installation check
A typical lighting condition requires a scheme to be submitted and approved before the relevant part of the development is occupied, with the scheme to include luminaire specifications, mounting heights, tilt angles, isolux contours and a maintenance regime. Some authorities add a requirement for post-installation verification: field measurements at identified windows, taken at night, after the installation has been commissioned.
Plan for that check. A design that sits at 95 per cent of the limit on paper will fail in the field once the real reflectances, the real mounting heights and the installer's preferred tilt are involved. Build in margin, and keep the commissioning records.
Where a Lighting Assessment is being drafted as part of an application, an AI-assisted draft can set out the zone argument, the receptor list, the policy framework and the condition wording, then go to the lighting designer for the photometric work. The professional directory is the route to a reviewer for that part.
Scoping it for a small scheme
Not every proposal needs both documents. A rough guide, treated as illustrative rather than a rule:
| Scheme | Usually sufficient |
|---|---|
| Domestic security lighting, suburban | Luminaire specification and a note on tilt and spill |
| Small car park, fewer than 20 spaces, urban | Lighting design with isolux contours and a short obtrusive light section |
| Floodlit sports pitch or arena | Full lighting design plus a standalone obtrusive light report and an ecological lighting note |
| Commercial yard or forecourt in E1 or E2 | Obtrusive light report against the agreed zone, with the design appended |
| Any scheme near a bat roost or dark corridor | Ecological lighting assessment alongside whichever of the above applies |
Illustrative example: a village pub proposes six 30 W floodlights over its car park. The applicant assumes E3, the council treats the location as E2, and the modelled vertical illuminance at two cottage bedroom windows exceeds the post-curfew limit. Changing to flat-glass luminaires at 4 m with a 0 degree tilt and a 23:00 switch-off brings both windows inside the limit, and the hedgerow at the rear is left unlit at the ecologist's request.
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. To see which lighting and ecology documents a site is likely to need, browse the report types on PlanScope.
Frequently asked questions
What is the difference between a lighting assessment and an obtrusive light report?
A lighting assessment is a design document showing that a space receives the illuminance its use requires, against a standard such as BS 5489-1 or BS EN 12464-2. An obtrusive light report is an impact document testing sky glow, light intrusion at windows, luminaire intensity and building luminance against the ILP environmental zone limits in GN01.
How is the ILP environmental zone decided?
It describes the receiving environment, from E0 for intrinsically dark areas through E1 rural, E2 low district brightness, E3 suburban and E4 urban centre. It should be agreed with the planning or environmental health officer at scoping, because councils often treat a village edge as E2 where an applicant has assumed E3, and the limits differ sharply.
What is a lighting curfew in a planning condition?
A time after which much tighter limits on light intrusion, luminaire intensity and sky glow apply. It is set locally and 23:00 is common, so check the council's own supplementary guidance rather than assuming. Many schemes meet the post-curfew limits only by switching off or dimming on a timer or sensor.
Do the ILP limits protect bats?
No. The environmental zone limits are about amenity and sky glow. Bats are dealt with through the joint ILP and Bat Conservation Trust guidance on artificial lighting, which covers spectrum, warm colour temperature, direction, shielding, part-night regimes and lux levels on commuting and foraging routes. Where a roost is identified, the ecologist must check the lighting design.
Will the council check the lighting after installation?
Some authorities condition a post-installation verification, with night-time field measurements at identified windows once the scheme is commissioned. Real reflectances, mounting heights and installer tilt angles rarely match the model exactly, so design with margin below the limit rather than at it, and keep the commissioning records.
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.