Sustainable By Design: Outdoor Lighting – Brighter Not Always Better
By Anne Cosgrove
Published in the February 2007 issue of Today’s Facility Manager
Outdoor lighting is a part of virtually every facility. Whether the goal of the illumination is for security, safety, or signage, an important issue for many is light pollution. Defined by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute as “the unwanted consequence of outdoor lighting, which includes such effects as sky glow, light trespass, and glare,” light pollution has evolved from being an annoyance to star gazers to a subject of legislation on local, state, and national scales.
Among the regulations passed into law, a common theme is to preserve the darkness of the night sky. As such, the enacted laws include parameters outlining maximum illumination allowed and advising what types of light fixtures and accessories should be used to operate within the regulations.
Facility managers embarking on exterior lighting projects should be aware at the outset of the laws and other guidelines that affect their sites. Paul Mitchell, a sales manager with Roselle, IL-based Sternberg Lighting, advises, “The regulations might be municipal, state, or federal ordinances. Facility managers should also check with the local Department of Transportation if their facilities are near a major thoroughfare or state truck line.”
Upon identifying the criteria impacting the site, facility managers can look for lighting fixtures that meet the physical, and any legal, requirements. This may include looking for lighting products that incorporate optics. These types of fixtures work to reduce the light to an acceptable level, thus reducing light pollution.
Sky glow, one cause of light pollution, is the brightening of the sky caused by both natural and man-made factors. Facilities with outdoor lighting are among the contributors to this condition. One way lighting manufacturers address this is with products featuring “cut-off” characteristics. Full cut-off means that the light emitted remains below the 90° horizontal plane, thus preventing light from unnecessarily shining upward. (There are also cut-off and semi cut-off products that allow more light to shine upward, but still reduce light pollution as compared to a non cut-off lamp.)
Commenting on the cut-off approach to outdoor lighting, Mitchell notes, “It is important to recognize that [the need to reduce or eliminate upward light] is not always present, and there are many applications where some uplight is preferred. However, more often than not, a facility manager will want to reduce the uplight to a reasonable level.”
Light trespass—another light pollution culprit—is light being cast where it is not wanted or needed, such as that from a streetlight or a floodlight that illuminates a neighboring building, thus causing uncomfortable conditions for the occupants in that building.
Several approaches can go a long way toward reducing light trespass. The first is to consider the surrounding area during the lighting design and to select luminaires, locations, and orientations that minimize the light that spills onto adjacent properties. Secondly, the project should specify luminaires that control the intensity (candela) distribution.
Glare is another issue to consider when concerned with light pollution. As defined by the LRC, glare is “the sensation produced by luminances within the visual field that are sufficiently greater than the luminance to which the eyes are adapted, which causes annoyance, discomfort, or loss in visual performance and visibility.” This condition can be caused by streetlights, parking lot lights, floodlights, signs, sports field lighting, and decorative and landscape lights.
Susan Anderson, manager, energy relations with OSRAM SYLVANIA in Danvers, MA, points out that in specifying luminaires for an exterior application, the facility manager should consider the location of the facility relative to other buildings, as well as roads. “If the lighting will be along a roadway,” says Anderson, “one should consider if cutoff is important to avoid glare in the eyes of passing drivers. And, with light pollution as an issue, it is also important that light from the site does not spill over onto an adjacent property or is visible from nearby properties such as a residential area.”
In response to the growing demand to reduce light pollution, research and development efforts have focused on advancements in technology to design luminaires that will efficiently direct light where it is needed. Many manufacturers have concentrated on providing efficient luminaires with sufficient beam distributions while meeting the cutoff classifications set forth by the Illuminating Engineering Society of North America (IESNA), a recognized authority on illumination.
Advancements in lamp technologies have resulted in producing higher efficiency light sources that not only reduce light pollution but also offer the added benefit of saving energy. Advises Anderson, “High pressure sodium (HPS), metal halide, fluorescent, and induction sources are all energy efficient options for exterior lighting. In general, HPS is the most efficient; however, it provides a yellow-white light not acceptable for all applications.” Where white light is desired, Anderson points to metal halide, fluorescent, and induction as possible light sources. “If considering metal halide, facility managers should look at the more energy efficient pulse start systems,” she adds.
When embarking on an outdoor lighting system project, facility managers will benefit by identifying what is required by law. Further research will enable the project to achieve energy efficient savings as well. Working with an experienced lighting designer may ensure that the most effective system is put in place.
This article includes interviews with Anderson and Mitchell. Information from the Lighting Research Center and IESNA was also included. A compilation of existing outdoor lighting laws is available from The International Dark-Sky Association.