Getting the light right

14th February 2014


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Sian Hepworth

Lee Gunner describes the potential impacts of obtrusive light from new developments and how they can be minimised

Writing his most famous poem Daffodils in the early 1800s, William Wordsworth described the stars as “a never-ending line”. “Ten thousand saw I at a glance,” he wrote, “tossing their heads in sprightly dance.” If Wordsworth were writing today, I wonder if he would use the same simile comparing a field of daffodils with the Milky Way. Given the issues surrounding light pollution, it seems unlikely.

The term “obtrusive light” has come about as a result of the steady urbanisation of natural landscapes and the human desire to extend day into night. It is used to describe poorly controlled and distributed artificial light, which results in adverse impacts to the surrounding environment. Obtrusive light impacts can include:

  • Sky glow: the upward spill of light into the sky, which can cause a glowing effect. This is often seen above cities when viewed from a dark area.
  • Light spill: the unwanted spillage of light onto adjacent areas, which may affect sensitive receptors, particularly residential properties and ecological sites.
  • Glare: the uncomfortable brightness of the light source against a dark background, which dazzles the observer. This may cause nuisance to residents and a hazard to road users.
  • Light trespass: the spilling of light beyond the boundary of a property, which may cause nuisance to others.

Policy and guidance

Guidance on controlling obtrusive light should have been implemented when Edison patented the first practical artificial light source in 1879. However, this key consideration was missed until it was noted that stars were gradually disappearing and bats were hiding or feasting on insects attracted to UV light at lampposts and ultimately becoming visible prey themselves.

Such observations during recent decades have resulted in a surge of policies to provide good practice guidance, and establish limits and measures to control obtrusive light. These have steadily been reviewed, revised and updated to provide the current legislation, national and local policies and guidance documents. In 2005, the Clean Neighbourhoods and Environment Act classified light emitted from a defined premises as being a statutory nuisance and allowed local authorities powers to deal with artificial lighting for certain types of premises.

Government policy on light pollution has evolved from various supplementary planning policy guidance documents to the national planning policy framework, which was published in March 2012. The NPPF encourages good design, with planning policies and decisions limiting the impact of light pollution from artificial light on local amenity, intrinsically dark landscapes and nature conservation.

Meanwhile, local authority policies vary considerably, with some councils providing simple cartoons of “dos and don’ts”, while others have extremely lengthy and detailed lighting strategies and supplementary planning guidance lists as long as your arm.

Guidance from other bodies, such as the Institute of Lighting Professionals (ILP) and Chartered Institution of Building Services Engineers, is steadily evolving in relation to updates to environmental impact assessment (EIA) legislation, improvements in technology and changing practitioner views. Key guidance documents are:

  • Guidance notes for the reduction of obtrusive light (GN01: 2011) produced by the ILP. GN01:2011 is the piece of guidance most commonly referred to in government policies, scoping opinions and condition clauses. It provides a list of lighting dos and don’ts, as well as design guidance limits to ascertain the acceptability of obtrusive light levels at night.
  • Guidance on undertaking environmental lighting impact assessments (PLG04) by the ILP.
  • Bats and Lighting in the UK. This guidance from the ILP and the Bat Conservation Trust is intended to raise awareness of the impact of lighting on bats and suggests mitigation for various scenarios.
  • Guide on the limitation of the effects of obtrusive light from outdoor lighting installations (CIE 150) produced by the International Commission on Illumination (CIE) and Guidelines for minimising sky glow (CIE 126). These documents provide guidelines for assessing the impacts of outdoor lighting.
  • Guide to limiting obtrusive light by the Chartered Institution of Building Services Engineers. This document contains guidance for planners and lighting designers regarding limiting obtrusive light and improving quality.

Impacts of obtrusive light

Obtrusive light has a number of impacts. These can vary in significance depending on the type and sensitivity of the receptor, which include: ecological, residential, employment, highway and landscape receptors.

Obtrusive light can affect ecological systems considerably through light trespass and sky glow. It is recognised that some species can be adversely affected to the point where they migrate or avoid foraging or roosting in a previously occupied area.

Research by Dr Emma Stone, for example, indicates that light pollution can have significant conservation consequences for threatened bat species, because of changes in the use of established flight routes and delayed commuting behaviour. This may force bats to use suboptimal routes, potentially causing isolation of preferred foraging sites. This must therefore be considered when artificial lighting is proposed within ecologically sensitive areas.

The effect of obtrusive light on residential developments, meanwhile, relates to the human response to light and its effect on visual performance and the circadian rhythm (the human “body clock”). Glare can be irritating, induce headaches and affect personal safety, while light trespass can affect sleep patterns and hormone levels, which in turn can induce insomnia. Daytime activities can also suffer in terms of performance and safety, both at home and in the workplace. A seated worker or a machine operator, for example, might be in a static working position for a long period and may be affected by obtrusive light glare. This could cause tiredness and affect safety. Glare is also the element of obtrusive light that can most seriously influence the visibility and welfare of road users. Highway lighting, meanwhile, can be a source of obtrusive light to surrounding areas.

The change in the night-time view caused by lighting in a new development is a subjective consideration that can form part of a landscape and visual impact assessment. The lighting system is a key component of the night view and increasing light trespass and glare to the surrounding environment can create a negative response from the local community and may even impact distant views through a change in sky glow, for example. Both can detract from the surroundings and if unchecked act as a negative precedent for future local development.

Mitigation measures

Guidance documents, such as those cited above, provide practical advice on standard mitigation measures. If applied at initial design stages, obtrusive light impact can be minimised, reducing the need for changes to the masterplan and alterations post-completion. Common mitigation measures employed at the design stage include:

  • Lights with a reduced UV wavelength. UV light is a characteristic of natural and artificial light that attracts insects. Sodium and LED light sources carry little UV light and minimise insect magnetism.
  • Flat-glass light distribution. This eliminates direct upwards light the primary contributor to sky glow.
  • Minimal column heights. This can reduce the light footprint and any consequential overspill. However, shorter columns invariably lead to an increased number of lighting points.
  • Switching off or dimming unnecessary lighting during unoccupied hours. Such measures should be subject to health and safety approval.
  • Light controlling shields. These provide a cut off to the light distribution. Within a good design scheme, these would be a last resort and are usually applied post-installation.
  • Planting and retention of trees onsite. Trees provide a natural method of screening and the best effects are achieved with dense, evergreen species.

Technological advances

Advances in the manufacture of light fittings and light-source technology have resulted in ranges suitable for the most sensitive of environments. For example, LEDs have the benefit of putting light only where it is wanted. Similarly, the recognition of white light, which provides improved visual acuity, allows for lower lighting levels and minimal UV wavelengths.

Such advances allow for tangibly lower levels of obtrusive light, but they usually carry a cost premium. If such mitigation measures are required in planning approvals, this may cause concern for the developer when the tender returns are assessed. Expert advice, at an early stage, can help to avoid a kneejerk reaction regarding costs by highlighting where advanced and traditional technologies are required, thereby ensuring minimal impact at planning approval.

Too often, attempts to limit obtrusive light have been misunderstood or fallen through the gaps, resulting in a detrimental impact on the environment.

Such failings could be due to fear of cost, inadequate policy or a lack of client knowledge and team expertise. The technical reports created by lighting professionals are sometimes not easily understood or translated into a format that fits with impact assessments prepared by others.

On a more positive note, improvements are constantly being made in the control of light and with these implemented we should see a steady reduction of obtrusive light and its effects.

Lee Gunner is an associate at Hoare Lea Lighting. For more information contact

* Image: Stars over Salzburg - shows the glow of the city's lights on a moonlit night. Taken from an Alpine vantage point, the photo reflects concerns regarding sky glow: the upward spill of light into the sky. © Andreas Max Böckle

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