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Bringing Back the Stars

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Photo 1. Los Angeles by night

Sky-glow-conscious lighting design is not something new. On the contrary, good lighting designers have been routinely taking sky glow into account for many years. Stray light escaping up into the sky represents poor design, a waste of energy, and a waste of money. It also prevents city dwellers from experiencing one of the most awesome and comforting sights that nature has to offer - the star-filled night sky.

Unfortunately, not all lighting installations are designed by qualified lighting designers. The profession, mainly through the work of CIE divisions 4 & 5, is therefore in the process of developing guidelines which, hopefully, will be published in 1996/97. This paper outlines some initial data and thoughts being put together by the CIE committees responsible. *

Before getting involved with light-technical parameters, the committee members felt that some environmental zones should be recognized and defined. This is an obvious need, as all would agree that what might be acceptable in light- pollution terms in the center of a capital city would not be acceptable in rural areas.

Table 1 suggests four zones, of which the last three have been designed to fit in with those already used in other aspects of exterior lighting design: Some groups, particularly the astronomers, would like more zones, and CIE TC 4.21 has proposed doubling this number to eight; however, this proposal is still under review.

LIGHT SOURCES
Astronomers would like to see more monochromatic, low-pressure sodium lighting so that they can easily "filter out" the sodium "D" lines from their telescopes and spectrometers. However, this solution is far from satisfactory for the rest of the population, many of whom have had enough of the "environmental pollution" of a different kind that this lamp has produced - that of a world devoid of all color except for orange and muddy greys. It is also worth noting that where the aim is to design luminaires producing low levels of light pollution it is much easier to use a high-pressure discharge lamp, due to its relatively small size, than a low-pressure sodium lamp (the 180-W type used for motorway lighting is over one meter long!). It is therefore suggested that in the vicinity of an astronomical observatory, a low-pressure sodium lamp be used, in line with the recommendations of CIE Document No. 1, while elsewhere, the smaller, more compact lamps should be preferred where light pollution is a consideration

LUMINAIRES
At the Lux Europa/CIE Symposium at the Edinburgh Royal Observatory in 1993, it was proposed that fixed-angle exterior luminaires be rated in terms of their light-polluting capacity, measured as the Upward Light Output Ratio (ULOR) and/or actual upward flux. So as not to promote inefficient luminaire designs, it was recently decided to use the Upward Waste Light Ratio (UWLR) instead, which brings the total light output ratio into the equation.

Table 2 shows some suggested limits taken from the UK Institution of Lighting Engineers "Guidance Notes for the Reduction of Light Pollution".

Whereas the above-suggested light pollution ratings should be of considerable help in reducing sky glow, it should be remembered that in some cases the overall level of pollution - as well as energy costs - would be lower when using a low number of "more polluting" luminaires than a larger number of "less polluting" ones. It is therefore hoped that these parameters can eventually be extended to include actual lumen figures.

The optical systems now being computer designed around the above-mentioned high-quality, high-efficiency lamps have produced some remarkable luminaires. Since this article is concerned with outdoor lighting, the following examples are all of exterior lighting products. However, similar styles can - and are - being adopted for the interior market.


Photos 2-5. Examples of traditional and contemporary, decorative designs for road-lighting luminaires that use modern, energy-efficient optial systems.

Examples of how central London's light pollution and energy bills were both reduced by improved optical control were presented at the IAEEL "Right Light Three" conference in 1995. This paper highlighted the relatively novel approach (for the early 1980s) of fitting high-tech optics within traditional, existing, street lanterns (see A Successful Retrofit). There are now a great many traditional, as well as contemporary, style street lights on the market that combine a well-designed daytime appearance with efficient nighttime illumination of the roadway.

Below are a number of simple graphic illustrations giving advice on right and wrong in designing for redced glare and sky glow:









(Source: Guidance Notes for the Reduction of Light Pollution, from the Institution of Lighting Engineers, UK.)

INSTALLATION DESIGN
Standards for outdoor lighting have existed for many years. Like most standards, however, they have generally been minimum requirements only, i.e. those required for security and safety of the required task.

Once these minimum levels had been met, no one seemed to worry about lighting anymore, the assumption being that simple economics would control that aspect. However, as explained previously, with the advent of modern light sources this approach is no longer working, particularly in the fields of security and commercial advertising.

In the field of decorative building lighting, particularly in major urban centers, the guiding principle for planners and designers seems to be similar to that of New York architects during the 1930s: "It must be higher than anything around it". Unfortunately, the cost of such a practice has not always been acknowledged in either aesthetic or energy terms - hence the current concern in lighting circles.

At a lighting seminar held in London in 1992, a well-respected lighting designer ventured that light meters and planned lighting levels had no place in lighting design philosophy and that the visual impression was all that mattered.

No one could argue that what finally matters is not the meter reading, but what we see. The problem, however, is that not many people can trust their eyes to be those of a standard observer, and personal views could very possibly be out of focus with the views of those around us. It is for these reasons that most lighting designers try to design lighting schemes around certain "agreed-upon standards". There is also a growing awareness that we cannot continue to overexploit the earth's finite resources simply because it appeals to us to do so.

The last thing that lighting design needs is a standard solution. Still, in the long term, it is imperative that we contain ourselves within sensible guidelines, especially in view of the environmental implications. Floodlight design has been rapidly improving. Thus for many of the luminaires available today the term "flood" is a misnomer since they no longer radiate light in all directions in order to flood their target with light. Of specific note are the asymmetric designs that permit the front glazing to remain at or near parallel to the plane of the surface being lit. This means that for most area, sports, and decorative building lighting, low light pollution goes hand in hand with the efficient use of energy.

Returning to the topic of urban lighting strategies, one of the major long-term aims is to develop an area-based lighting design system that integrates street-lighting design and decorative building/feature lighting. However, special care is needed here to ensure that this most laudable aim of achieving good visual design does not overshadow the importance of energy conservation.

At present, most of the design standards for highway lighting and decorative building lighting are published separately. However, both the CIE Urban Lighting Guide (Pub. No. 92) and the British Standard on Urban Centre and Public Amenity Areas, (BS 5489, Part 9) have started the move to bring them together.

Within the UK the Institution of Lighting Engineers (ILE) and the Lighting Division of the Chartered Institution of Building Services Engineers (CIBSE) have worked together to produce an "Urban Lighting Guide" with an up-to-date description of urban lighting strategies. The guide promotes an approach in which all lighting at a given location is proportioned into its functional, architectural, amenity and promotional components, and thereby suggests that no installation can be regarded as purely one of the above, but always a mixture of the four. This approach, in turn, encourages designers to consider lighting systems from a more holistic perspective.

As the millennium approaches, the lighting profession is becoming increasingly adept at enhancing the nighttime environment and reducing energy at the same time.

Nigel Pollard

The author is a lighting designer at: NEP Lighting Consultancy, Bath BA1 5NY, UK.
Fax: +44 1225 338 937,
E-mail: 106037.206@compuserve.com

References:

• *CIE Technical committee (TC) 4.21 Guidelines for minimising sky glow (4th Draft), and CIE TC 5.12 Guide on the limitation of the effects of obtrusive light from outdoor lighting installations (3rd Draft)
  
  
• ILE/CIBSE Lighting the Environment: A guide to good urban lighting
  CIBSE, Delta House,
  222 Balham High Road, London SW12 9BS, UK
  Fax: +44 181 673 3302

• The Right Light Three Proceedings contain papers on the subject.
  To order, contact: Right Light Three/Mrs. Grundy
  Northern Electric, Carliol House, Market Street
  Newcastle-upon-Tyne NE1 6NE, UK
  Tel: +44 191 210 2825
  Fax: +44 191 210 2898