Obtrusive light onto neighbouring windows
Light intrusion, glare and sky glow are three different effects measured three different ways. Knowing which environmental zone your home sits in decides every number in the assessment.
Light pollution from a neighbouring development is assessed in planning against published limits that depend on where you live, and the measurement that matters for a bedroom window is vertical illuminance in lux at the face of the glass. A floodlit car park next to a village will be held to a far tighter figure than the same car park in a town centre, because the guidance divides England into environmental zones and sets a different limit for each. Knowing which zone your home sits in is the first step in an objection that an officer can act on.
The rest of this explains how the assessment works and what to put in a representation.
What obtrusive light means
Guidance separates the effects of artificial light into three kinds, and they need different evidence.
Light intrusion, sometimes called light trespass, is spill light falling where it is not wanted, typically onto a window. Glare is the discomfort or disability caused by looking towards a bright source, which depends on the luminous intensity of the fitting in your direction rather than on how much light reaches the window. Sky glow is the brightening of the night sky by upward light, which affects the character of an area rather than any individual property.
A complaint about a security light shining into a bedroom is a light intrusion complaint. A complaint that a new sign is dazzling when you turn out of your drive is a glare complaint. The two are measured differently, and an objection that mixes them is easier for an applicant to dismiss.
National planning guidance on light pollution treats artificial light as a material consideration where it affects amenity, wildlife or the intrinsic character of an area, so all three effects are legitimately in scope.
Environmental zones and the limits for each
The framework most councils use comes from the Institution of Lighting Professionals guidance on reducing obtrusive light. It sets five environmental zones and gives numerical limits for each.
| Zone | Character | Vertical illuminance before curfew | After curfew |
|---|---|---|---|
| E0 | Protected dark sky areas | 0 lux | 0 lux |
| E1 | Intrinsically dark, National Parks and National Landscapes | 2 lux | 0 lux |
| E2 | Low district brightness, rural and small villages | 5 lux | 1 lux |
| E3 | Medium district brightness, suburban | 10 lux | 2 lux |
| E4 | High district brightness, town and city centres | 25 lux | 5 lux |
The zone is a judgement about the area, not a designation you can look up on a national map. Applicants sometimes assign a scheme to E3 when the receiving houses sit in what is plainly an E2 setting, and that single choice changes the acceptable spill by a factor of two. Challenging the zone is often the most effective point an objector can make, because every number in the assessment flows from it.
Upward light is controlled separately, expressed as the proportion of a luminaire's output emitted above the horizontal, and the permitted proportion falls to zero in the darkest zones.
Light trespass into windows and how it is measured
Vertical illuminance is measured in the plane of the window, normally at its centre, with the sensor facing outwards towards the light source.
The figure that counts is the contribution from the development, so the assessment takes a reading with the lighting on and a reading with it off, and reports the difference. That matters where a street light already lights the window: the applicant is responsible for their addition, not for the existing baseline.
Anyone can take a useful reading. A hand-held illuminance instrument costs very little, and a set of readings taken at the same window on several nights, with times and weather noted, is far stronger evidence than a description of the light being "very bright". Photographs help too, provided you say what camera settings were used, because an exposure chosen to show the glare exaggerates it and one chosen for the room hides it.
Where the effect is on outlook and general amenity rather than on measurable light levels, the argument runs on the same ground as outlook and sense of enclosure, and it is weaker but not worthless.
Glare and sky glow as separate effects
Glare is assessed on the luminous intensity of the fitting in the direction of the viewer, measured in candelas, with limits that fall sharply after curfew and in darker zones.
The practical cures are aiming and shielding. A floodlight tilted above the horizontal throws light and glare far beyond the area it is meant to serve, and the same fitting aimed downwards with a louvre or a shield can meet the limits without any reduction in the light on the ground. When you object, ask for the tilt angles and the shielding to be specified, because those are the details that get omitted from a lighting drawing.
Sky glow matters most in and around National Parks, National Landscapes and dark sky places, where policies are written to protect the darkness itself. Upward light from unshielded fittings, and light reflected off bright surfaces, both contribute.
Colour temperature is worth raising alongside all this. Warmer light at 3000 kelvin or below is less disruptive to sleep and to wildlife than cooler white light, and bats in particular avoid lit corridors. Conditions specifying maximum colour temperature are now common where a scheme is near a hedgerow, a watercourse or a known bat route.
Curfews and what changes after them
The curfew is the time after which the tighter limits apply, commonly 11pm, and it is set by the local authority rather than nationally.
After curfew the permitted vertical illuminance drops to a fraction of the daytime figure and, in the darkest zones, to zero. That means a lighting scheme which is acceptable at 9pm may be unlawful at midnight unless it switches off, dims or is controlled by detection.
Ask for the control strategy in writing. A scheme relying on movement detection needs the detection zones, the timeout period and the dimmed level stated, otherwise a single cat walking across a car park relights the whole site at 2am. This is the sort of detail a Lighting Assessment should already contain, and councils usually expect a suitably qualified author for that work, with professional review strongly advised.
Making an objection the officer can use
Objections that work are specific about the property, the effect and the remedy.
A useful representation contains:
- Your address and which window or windows are affected, with the direction they face.
- The environmental zone you say applies, and why, with reference to the character of the area.
- The effect described in ordinary terms, plus any lux readings with dates and times.
- The specific fittings on the submitted drawing that cause the problem, by reference number.
- What you are asking for: a curfew, a reduction in mounting height, shielding, a change of aiming angle or relocation of a fitting.
Avoid arguing that the development should be refused because of light alone unless the harm is severe. Lighting is nearly always conditionable, and an officer who cannot refuse will look for a condition. Giving them the condition you want is more productive than asking for an outcome they cannot deliver.
If the scheme is already built and the lighting is causing a problem, artificial light emitted from premises can amount to a statutory nuisance under the Environmental Protection Act 1990, with certain premises exempt. That route runs through environmental health rather than planning.
Conditions that actually control lighting
A lighting condition that says "external lighting shall be designed to minimise light spill" controls nothing, because nobody can measure compliance with it.
The conditions that work require a scheme to be submitted and approved before installation, containing a luminaire schedule with manufacturer data, mounting heights, aiming angles, iso-lux contour plots showing predicted vertical illuminance at named neighbouring windows, the curfew and control strategy, and the maximum colour temperature. Then they require the approved scheme to be installed and retained.
Ask for the iso-lux plots specifically. They are the drawing that shows whether the limits are met at your window, and their absence from a submission is the clearest sign that the assessment has not been done properly. Where daylight rather than artificial light is the concern, a Daylight and Sunlight Assessment is the equivalent document.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified 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.
Frequently asked questions
How is light spill onto my window measured?
As vertical illuminance in lux, measured in the plane of the window and normally at its centre, with the meter facing outwards. The assessment takes a reading with the development's lighting on and one with it off, and reports the difference, because the applicant is responsible for their contribution rather than the existing baseline.
What are the environmental zones?
Five categories running from E0 for protected dark sky areas through E1 for intrinsically dark areas such as National Parks, E2 for rural and village settings, E3 for suburban areas and E4 for town and city centres. Each has its own limit for vertical illuminance at a window, before and after curfew.
Can I challenge the zone the applicant has used?
Yes, and it is often the strongest point available. The zone is a judgement about the character of the area rather than a mapped designation. Moving a scheme from E3 to E2 halves the acceptable spill at your window, and every other figure in the assessment follows from that classification.
What is a lighting curfew?
The time after which tighter limits apply, commonly 11pm and set by the local authority rather than nationally. After curfew the permitted vertical illuminance falls to a fraction of the earlier figure, and to zero in the darkest zones, so the scheme must switch off, dim or be controlled by detection.
Which lighting condition is worth asking for?
One requiring a scheme to be approved before installation, with a luminaire schedule, mounting heights, aiming angles, iso-lux contour plots showing predicted illuminance at named neighbouring windows, the curfew and control strategy and a maximum colour temperature, then requiring that scheme to be installed and retained.
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.