Light spill into bedroom windows and the curfew hour

If a new floodlight, car park lamp or illuminated sign is shining into your bedroom, the measurement that matters is vertical illuminance at the window, expressed in lux. Guidance Note 1 from the Institution of Lighting Professionals sets limits for that figure by environmental zone, and it sets a much tighter limit after a curfew hour, which in most places is 23:00. A scheme that is acceptable at 9pm in a town centre can be well outside the guidance at midnight in a village.

That gives an objector something precise to say. Rather than describing the light as too bright, you can name the zone, name the limit and ask for a condition that holds the applicant to it.

What vertical illuminance at a window measures

Vertical illuminance is the amount of light falling on a vertical plane, measured at the window of the property affected rather than at the light source. It is the quantity that corresponds to what you experience as light intrusion.

It is measured in the plane of the glass, usually at the centre of the window, with the light source operating and then with it off so the difference can be attributed. The guidance limits refer to light from the development in question, so the background reading from street lighting and other sources is subtracted.

Two other quantities appear alongside it in lighting reports. Luminaire intensity, in candelas, towards a potential observer at the window, which governs glare rather than overall brightness. And upward light ratio, the proportion of a fitting's output going above the horizontal, which governs sky glow rather than intrusion into a room.

Environmental zones and how the limits change

The guidance divides the country into zones by how dark the area is at night, running from protected dark areas through intrinsically dark rural landscapes, low and medium brightness districts, and finally high brightness urban centres.

The zone is a judgement, and applicants and objectors often disagree about it. A village on the edge of a town is commonly claimed as E3 by the applicant and argued as E2 by residents, and the difference halves the permitted figure. Base your position on the character of the area at night rather than on the planning designation, and say why.

Note that the post-curfew figure in a dark rural zone is zero. Not low. Zero. That is the strongest point available to anyone objecting to a floodlit facility in open countryside.

The curfew hour and part night dimming

Curfew is the time after which the stricter limits apply. The guidance does not fix the hour itself, and the local authority sets it, with 23:00 the most common choice. Some authorities use 22:00 in residential areas and later hours for town centre schemes.

The practical response is part night operation. Modern external lighting is controlled by a time clock or a management system, so an applicant can be required to reduce output or switch off entirely at the curfew hour. Dimming to a set percentage is a weaker control than switching off, because the residual level is often still above the post-curfew limit in a dark zone.

Security lighting is the exception argued most often. A reasonable compromise is low level permanent lighting within the limits, with higher output on detection, aimed and shielded so the detection zone does not include a neighbouring garden. Detectors triggered by passing traffic are a frequent source of complaint and are usually a siting error rather than a specification one.

Luminaire intensity and the glare limit

Light intrusion and glare are different experiences. A distant floodlight can produce a modest lux reading at the window and still be intolerable because the source itself is visible and bright against a dark background.

The guidance deals with this through a limit on luminous intensity in candelas in the direction of the observer, and it tightens sharply after curfew. The practical fixes are shielding, aiming and mounting height. A flat glass, fully cut-off fitting aimed below the horizontal produces far less glare than a tilted floodlight with exposed optics, and it also reduces sky glow at the same time, which is the subject of sky glow, dark skies and upward light ratio.

If a lighting report gives only lux figures and says nothing about intensity towards specific windows, that is a gap worth raising.

Measuring light spill at an existing property

You can take useful readings yourself with an inexpensive lux meter, provided you record the method.

1. Wait for full darkness, well after sunset, with no moonlight interference noted.
2. Hold the meter flat against the glass of the affected window, sensor facing outwards.
3. Record a reading with the source on, then with it off if that is possible, or at a time when it is off.
4. Note the date, time, weather, the meter model and the exact window.
5. Repeat on a second night to confirm.

Photographs taken from the same point with a fixed exposure are a useful supplement and are more persuasive to a committee than numbers alone. A phone photograph on automatic exposure proves nothing, because the camera compensates.

Where the lighting is already installed and causing a problem, there is a second route alongside planning. Artificial light emitted from premises so as to be prejudicial to health or a nuisance is a statutory nuisance under the Environmental Protection Act 1990, with exemptions for certain premises including transport facilities. The environmental health team investigates, and that route can be quicker than an enforcement complaint.

Raising it as an objection with evidence

Light pollution is a material planning consideration, and Planning Practice Guidance has a chapter on it. An objection that names the zone, the applicable limit and the window affected is read differently from one that says the lighting will be intrusive.

Set out four things. The zone you say applies and why. The windows affected, with their use, because a bedroom carries more weight than a hallway. The figures from the applicant's own lighting report at those windows, if there is one. And the specific condition you want imposed.

Where no lighting report has been submitted and the scheme obviously involves external lighting, ask for one. A Lighting Assessment with isolux contours at the boundary and at named windows is the document that lets the officer judge the issue, and its absence is a reasonable ground to ask for deferral. Noise from the same development is often raised alongside light, and a Noise Impact Assessment covers that separately.

Conditions that control it effectively

A good lighting condition has five elements: a requirement for a detailed lighting scheme to be approved before the lighting is installed, a stated design standard referencing the guidance and the environmental zone, numerical limits at named windows, a curfew time with the operating regime after it, and a post-installation verification report.

Weak conditions say the lighting shall be designed to minimise light spill. That is unenforceable, because nobody can say what minimise means at 1am. Ask for numbers and a named window.

Verification matters more than the design. Fittings get substituted on site, aiming angles drift and time clocks get reset, so a condition requiring a post-installation survey submitted to the authority within a set period after first use is what makes the rest of it real.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.

Browse the PlanScope report library to see which environmental reports a development with external lighting is likely to need.

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