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Out & about - A framework for exterior lighting design

The following paper was presented to the National Lighting Conference held at York University in July 2000.

This paper sets out a lighting design framework for the design and assessment of exterior lighting schemes. It identifies the need to clearly think out and state the objectives of any lighting scheme. Then the ways to achieve these objectives can be considered and weighed against the possible adverse affects of the scheme.

By carefully considering the objectives, correctly selecting and siting the equipment and minimising the possible adverse features a successful exterior lighting scheme can be created without undue criticism or objections by those living near by.

Introduction

The lighting of buildings, roads, sports fields, signs and car parks affect those who use them, live by them or view them at night. Exterior lighting may enhance parts of our world, but may also cause glare, cause annoyance by light intruding into our homes or waste unnecessary amounts of energy and therefore money. The poles, columns, brackets and lights all remain visible during the day and may be unsightly.

In all decisions about the lighting of areas or features within our environment we need to weigh-up the advantages of lighting with the possible adverse affects on some aspect of that environment. The over emphasis of any one factor is likely to lead to a greater affect on the others and may even result in the lighting scheme not meeting the original objectives for installing it. A balanced approach is needed to achieve a high quality lit environment for all of us to enjoy and benefit from.

The presentation will discuss these various factors and will examine the balances that need to be struck between them in different cases. The weighting of the factors for the lighting of a factory car park will vary depending on whether it is next to a country park or an industrial park. The lighting of a tennis court in a particular location may be justifiable if it is in full time use by the local community around it, but perhaps not if it is for the occasional use by one family.

The design objectives

The objectives of any design should be carefully thought out at the outset. For a private outdoor tennis court this may be as simple as ‘To play casual tennis during the evenings’. For a public tennis court it may be ‘To play competition standard tennis after dark’ or ‘To enable tennis coaching after dark’. Each of these objectives carries slightly different requirements regarding lighting levels and quality as well as differing levels of need.

For a scheme that may be regarded as decorative the objectives are just as important. For a public building these may be ‘To enhance the status and presence of the Town Hall at night’ or ‘To highlight the architectural features of the Town Hall after dark’. Again, both of these objectives would warrant a different lighting scheme and the way that the scheme uses energy and its effect on the surroundings would need to be judged differently.

For a more complex project the objectives would need to be more detailed. Thus the exterior lighting of a supermarket would be split into a number of sectors covering security, safety of movement around the site, safety of truck unloading, attractive lighting of the customer car park, decorative lighting of the public facades and possibly distinctiveness of the lighting system itself.

These are some of the criteria that may be used in creating the objectives:

  • Lighting levels fall into two categories: lighting for tasks and lighting for display. The lighting level needed for a given task, along with other criteria such as uniformity, can be found from the relevant standard or lighting guide such as ‘The Industrial Environment’1, ‘Sports Lighting’2 and ‘The Outdoor Environment’3. For areas being lit for display or effect the levels need to be selected with knowledge of the surrounding district brightness so that the area being lit has the correct prominence within its surroundings.
  • Cost limitation is often a major objective of a lighting scheme. The need to provide a scheme for a low initial cost is a challenge but should be tackled in a way that produces a cost-effective solution. The long term operating costs should not be allowed to become unacceptable just to meet an initial cost.
  • Glare control is often an important criterion near to surrounding properties or by transport routes. Over-spill of light from a scheme should not be allowed to intrude into neighbouring properties or to cause annoyance to neighbours. Special consideration is always needed near to roads, railways, ports and airports.
  • Colour of the light is often specified to create a specific effect or feeling. A contrast in colour with the lighting of the surroundings can often be more impressive then a higher lighting level.
  • Maintenance requirements may be most important in remote or difficult situations. Lighting the outer wall of a castle on top of some dramatic cliffs may also require the maintenance staff to perform some equally dramatic manoeuvres to replace lamps.
  • Safety or security needs may be given as the main criteria of scheme. For the perimeter lighting of a high security establishment or the lighting of the access walkways around a refinery security and safety are prime lighting objectives.
  • Visual effect can be an important objective either in terms of providing high impact for something like an advertising sign or in a dramatic or subtle lighting of a monument.
  • Low energy usage is often given as an objective of a design without much consideration as to what would be a low value. Whilst minimal energy use to achieve the other objectives of the scheme is desirable low energy use as a prime objective often leads to a compromised lighting solution.

The Design Framework

In trying to meet the objectives of a scheme the designer needs to select various design components in a way that minimises the possible adverse effects of the lighting scheme on the environment and on surrounding users.

There is always a balance to be struck between the various options. Each decision made in fulfilling the objectives of the scheme will have positive and negative effects.

Design components

There are various components in a lighting scheme that a designer uses to achieve the objectives of a project. Some are truly physical components, such as the luminaires or lamp chosen and others are more abstract properties such as the aiming of the lights or the lighting levels chosen.

Each of these components needs to be considered carefully so that the objectives are met in the most efficient and economic way with least adverse or unwanted impact on the surroundings.

  • Luminaire choice is significant in setting the efficiency of production and spread of light on a project. Some types of luminaire are very precise in their beam spread and others can cover a wider area, but with more spillage. The daytime visual impact of the luminaire must also be considered.
  • The position of the lighting equipment not only determines the lit appearance of the building, area or object being lit, but affects the visibility of the lighting from the surrounding area, the spill of light into the night sky and onto adjoining properties.
  • The choice of lamps will affect the colour of the lighting, the appearance of the object or area being lit and the energy usage. Light with a high colour rendering index, such as metal halide and white SON (high pressure sodium), are far more acceptable to the general public than low pressure sodium. They enhance the recognition of faces and car colours in the street leading to a greater sense of security.
  • The aiming of each luminaire is most important if accurate lighting levels and drop-off of light are to be achieved. Thought needs to be given to ensure that the luminaires can be re-lamped by maintenance staff without affecting the aim of the luminaires. Many accurately aimed schemes are ruined by the luminaires being re-lamped and inexpertly re-aimed.
  • The use of shutters and baffles may be needed to keep the light from a specific luminaire from spoiling the effect of the lighting by reducing the contrast of the lit object or by allowing light of one colour to spill onto an area lit by another colour. Lenses can be used to spread light into and oval or to diffuse or concentrate light as required to meet an objective or to compensate for lack of sufficient light control from a luminaire. Appropriate use of shutters, baffles and lenses can lead to a more effective scheme with fewer adverse effects.
  • The control system should chosen to suit the timing of the on periods of the various parts of the lighting. Where light is needed at all hours of darkness then simple photocell control is preferable. Where lighting is only required in the evenings or on certain days then either a standard time-clock or a solar-dial time-clock is needed. More complex effects lighting may need programmed lighting controllers to be effective. Excessive hours of use of a lighting scheme is not only increases energy and lamp usage but may lead to greater complaints from those living or working nearby.

Whilst each of these components contributes to meeting the objectives of the scheme each may also have an unintended adverse effects on the surroundings. The selection of large luminaires may affect the daytime visual impact of the scheme. A high overall lighting level may make the scheme too prominent in its environment. Poorly thought out aiming may lead to light trespass to neighbouring properties.

Adverse effects

There are a number of possible adverse factors that need to be considered when trying to meet the objectives of a lighting project. Not all are relevant to every project and each will carry different weighting depending upon the exact nature of the project and its location.

These factors include:

Several of these factors are discussed in more detail below.

1. Visual impact of the lighting equipment during the day

  • Large luminaires may be more efficient but they may also have an adverse effect on the daytime visual impact of a lighting scheme.
  • Where efficient design results in lighting being mounted on high poles or towers these may be visually intrusive during the day. Lighting at high level can normally be seen from a great distance, especially in rural areas. There may also be restrictions on mounting lights on or by listed buildings or in conservation areas.
  • Louvres and baffles are often used to reduce light spill, but may also mean that the light fitting itself is less acceptable in appearance during the day.
  • Lighting from sunken pits can reduce the visual impact of the installation during the day, but may result in more overshoot of light into the night sky unless accurate masking or baffling is used.

2. Effect of light spillage on surroundings

  • Light spillage can be both annoying and wasteful. For neighbouring properties any spill light can be intrusive or unwanted. Stray light may prevent neighbours from sleeping or degrade a lighting scheme of an adjacent building.
  • An over-lit building or the light ‘missing’ its target can be obvious from a great distance.

3. Energy usage

  • It is taken that if a scheme is worthy of being carried out then a certain energy use is necessary. What is not acceptable is for unnecessary amounts of energy to be used.
  • Over lighting the building or area, either in terms of lighting too much or to a higher lighting level than is necessary, will use unnecessary amounts of energy.
  • Allowing unacceptable amounts of waste light either by poor aiming or poor luminaire selection leading to too wide a beam spread will also waste energy.

4. Light colour

  • The monochromatic low pressure sodium light whilst being more energy efficient, is not really acceptable in residential, shopping or work areas. Astronomers can however filter it out more easily from the sky glow.
  • In rural areas monochromatic lights are very obvious and intrusive and should not in general be used where visible from the surrounding countryside or domestic properties.

5. Effect of the light on animal and plant species

  • High levels of light at night can affect some animal and plant species by confusing the diurnal cycle of night and day that they set their internal clocks and biological processes by.
  • The natural day-night cycles of most animals and plants seem less affected by low-pressure sodium lighting.
  • Care must be taken in rural areas and close to parks and other wildlife areas to minimise unnecessary lighting.

6. Interference with adjacent transport routes

  • Lighting must not be allowed to interfere in the safe operation of transport routes.
  • Undue glare near to roads can reduce object visibility on and near to the road.
  • Direct glare along the line of a railway track or along a flight path to a runway can reduce the visibility of signals or approach lights.

7.Safety and health

  • Where safety requires it then lighting at the appropriate level should be provided.
  • Equipment that is accessible to the public should not be too hot to touch or be a physical danger to them.
  • Accessible towers should have appropriate anti-climb measures applied to prevent access by children or vandals.

8. Maintainability

  • Lighting must always be designed with safe maintenance in mind.
  • All equipment must be accessible for cleaning and re-lamping as required.
  • Lighting that is not easily accessible will rapidly decay both in terms of quality and in appearance.

There will be other possible negative factors for certain schemes that are not mentioned above.

  • risk of fire or explosion in a dusty or inflammable atmosphere
  • attracting vandals to a previously unlit area
  • appearance of modern equipment in a conservation area

Each scheme must be assessed based on its own particular characteristics and objectives.

In creating any new scheme all possible adverse effects must be weighed against the perceived benefits.

Conclusions

The objectives of any exterior lighting scheme need to be clearly stated or thought out before design commences.

The lighting equipment, their positions, aiming and control must all be chosen primarily to meet those objectives and not to meet other general criteria that the designer may think useful to add on. Of course, if having met the main objectives in the most efficient and economic way there are other benefits that do not cause adverse effects then they should be welcomed.

The scheme should not cause unacceptable adverse effects on the surroundings. These factors will vary in importance depending on the type of lighting and the location. The lighting of a pub car park in a town will have different problem to a similar one in a National Park even if the objectives are identical.

References and bibliography

1. ‘The Industrial Environment’ CIBSE Lighting Guide LG1, 1989.

2. ‘Sports Lighting’ CIBSE Lighting Guide LG4, 1990.

3. ‘The Outdoor Environment’ CIBSE Lighting Guide LG6, 1992.

4. ‘Environmental considerations for exterior lighting’ CIBSE Factfile 7, 1998.

5. ‘Lighting the environment. A guide to good urban lighting’ CIBSE/ILE, 1996.

6. ‘Road lighting in the environment’ DETR, 1993

7. ‘Lighting in the Countryside. Towards good practice’ The Countryside Commission, 1997.

8. ‘Guidance notes for the reduction of light pollution’ ILE, 1994.

9. ‘Guidance for minimising sky glow’ CIE publication 126, 1997.

Note: The three diagrams re-produced here are the copyright of Building Services Publications and were from their version of the above paper produced in the August 2000 edition of Light and Lighting magazine.

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