Balanced Beams

Outdoor sports field lighting design must satisfy end-user safety requirements without sacrificing the quality of life of neighboring residents.

In Seattle, an initiative to double the number of athletic fields citywide has been met with both resistance and resolution. Rather than develop new fields, city officials determined that extending the use of existing fields is the best way to meet rising demand. Similarly, in the Puget Sound region, developing fields with synthetic turf and artificial lighting systems has emerged as the most attractive option for parks departments and school districts to provide additional field capacity at minimal cost.

The Northwest is not alone. Illuminated sports field installations are at an all-time high nationwide. But to meet the minimum light-level requirements for safe nighttime play, high-wattage lamps and tall poles are specified for such projects. Consequently, the resulting lighting systems - often visible from great distances - dominate the evening landscape in both urban and rural settings. While these systems provide local teams unprecedented access to fields, they often yield undesirable side effects - commonly referred to within the lighting industry as light pollution, which includes light trespass, glare and sky glow.

Local residents typically want to know in advance of a new installation how the lighting will affect their neighborhood. Will light from the system enter their bedrooms at night? Will tall poles and bright luminaires pierce their panoramic nighttime views? Facility designers and ultimately operators are thus challenged to curb light pollution generated by athletic field lighting systems without compromising player safety and enjoyment.

How can this balance be achieved? Balancing proper light levels and sufficient field access against community concerns regarding excessive use of a lighting system and its potential side effects becomes a matter of combining the best available lighting equipment with the best possible system design. Clear assessments of the surrounding topography, vegetation and residential layout should be made before selecting lighting equipment. The extent of potential light pollution then needs to be analyzed to determine impact on the surrounding community.

Modern sports lighting has evolved from banks of unshielded floodlights to more-efficient and effective lighting systems. Manufacturers are now providing full-cutoff lighting systems, as well as floodlights with improved reflector designs and better shielding. The goal of each of these systems is to direct more light to the field and less into the surrounding environment.

Light trespass involves light entering an area, such as the bedroom of a neighboring home, where it doesn't belong. The potential impact of light trespass generated by a lighting system can be calculated in advance of installation using commercial lighting design software.

The performance of proposed lighting systems, including the type of luminaire specified, can be modeled using lighting equipment photometry provided by the equipment manufacturer. Pole locations and heights, luminaire quantities and beam spreads are selected and plugged into the computerized model. Property lines are identified and the amount of light trespass around the facility is calculated. The lighting designer can even run calculations based on different criteria, such as horizontal or vertical light. (Horizontal light is light that falls on a horizontal plane or surface, such as a playing field. Vertical light falls on a vertical plane or surface, such as a wall.)

To reduce spill lighting, luminaires specifically designed to provide better lighting control can be installed. Poles can be oriented so that floodlights are aimed away from sensitive areas. Additional poles may also be used to help reduce floodlight distance requirements, providing steeper aiming angles and more effective use of external shields.

Once the lighting system is installed, spill lighting is measured using a standard light meter, and readings are checked against the performance projections generated by the computer model. Field operators may then solicit input from local residents and provide additional adjustments to the aiming of floodlights to further minimize problematic impacts that have been identified.

Glare, meanwhile, is the result of lighting so intense - either pitted directly from a luminaire or reflected off the playing surface - that it causes discomfort for the viewer or impairs his or her vision. Glare is more difficult to quantify and measure, and it is dependent upon many different factors, including distance between an observer and the viewable object, brightness of the light source and amount of background illumination - to name a few. To assess the potential impacts from glare, engineers and designers can conduct photographic comparisons of existing lighting systems using similar vantage points. Computer simulations may also be used to estimate the amount of brightness generated by a bank of floodlights. Unfortunately, these methods produce outputs that can vary greatly or be skewed by individuals preparing the simulations to fit their specific agendas.

Finally, sky glow refers to light cast upward into the night sky, often obscuring one's ability to see stars. The extent to which sky glow impacts the environment is dependent on how much humidity or particulate matter is in the air for the light to strike, as well as the existing amount of light produced in the site's immediate proximity. Currently, there is no recognized industry standard to measure or quantify sky glow. The best way to gauge potential sky glow impact is to make nighttime visits under varying weather conditions to facilities that use similar equipment.

As manufacturers continue to improve equipment performance, thus providing lighting engineers with more design options, many municipalities are adopting their own design guidelines to reduce local light pollution. Common today are city ordinances and environmental regulations that require communities to be notified and involved in the process of approving new sports lighting systems. Dark-sky advocates, too, are championing regulations that target light pollution. Lighting designers and engineers are now expected to have knowledge of land-use policy and the permit-acquisition process. Gone are the days when the only requirement to construct an athletic field lighting system was to obtain an electrical permit.

However, determining how ordinances apply to the lighting of athletic fields can be tricky. Many new ordinances have been written without considering the demands placed on athletic field lighting systems. For example, lighting designers are often required by ordinance to use only full-cutoff lighting equipment, limit light trespass or restrict pole heights. Under these circumstances, a variance may be required to properly light a given athletic field. Every project has different requirements depending on the field's use and location. Choosing the right equipment is the first step toward properly lighting a field for its intended use. There are two luminaire types available today that can meet these demands while helping reduce negative environmental impacts: full-cutoff luminaries and shielded floodlights.

Sky glow and glare are significantly reduced by installing full-cutoff luminaires, or "shoebox lights." With these luminaires, no direct light is pitted above the plane of the luminaire. They are best suited for competitive and recreational fields that do not require extremely high lighting levels. They are not applicable to large fields with pole locations that require light to be projected long distances. Requirements for play must also be considered. For example, night baseball requires the illumination of a small object traveling at high speeds and at great heights. Downward-facing full-cutoff luminaires create a noticeable zone of darkness above the playing field, and the visibility of high fly balls can be affected.

Shielded floodlights also reduce light pollution through efficient reflector designs that help deliver more light from the floodlight to the field and less into adjacent properties and the atmosphere. Coupled with the use of large external visors, these floodlights do an excellent job of controlling spill light while also reducing glare and sky glow.

The recent design of three soccer field lighting projects in Seattle yielded three different results. One field's existing lighting system produced more than six foot-candles (vertical) of light trespass into several adjacent residential lots. However, retrofitting the system with shielded floodlights reduced light trespass to less than one foot-candle (vertical), thus meeting the city's newly established lighting guidelines.

Neighbors of a second set of fields scheduled to receive a new lighting installation requested that their territorial views be impacted as little as possible. To accommodate such a request, shielded floodlights were used to project the light greater distances, thus keeping the quantity of poles needed to adequately light the fields to a minimum.

A primary goal at the third site was to reduce glare from the lights as much as possible, since many of the residences surrounding the facility are set at higher elevations than the field. Full-cutoff luminaires were selected to reduce sky glow and eliminate all direct glare for residences situated on high ground above the lights, while significantly reducing glare for those at lower elevations.

Equipment selection and lighting design are critical to any new installation, but the ongoing operation of athletic field lighting systems presents its own challenges. Systems featuring site-based switches and programmable time clocks require personnel to manually alter programming or turn field lights on and off by hand. Should staff be unavailable to perform these functions, lights may be allowed to stay on even after fields are vacated or beyond established curfews. This inevitably generates complaints from neighbors who do not want to see the lights powered up during down times. Additional complaints often stem from the unnecessary use of electricity under said circumstances.

Field operators can now opt for more-effective, low-cost design solutions that provide better management of lighting systems. Lighting systems can be programmed using the same computer-based irrigation control systems already employed by many parks departments and school districts. By adding a control panel at the site that can be operated via a dedicated phone line (a land line or wireless connection), field operators have the capability to centrally program the lights to automatically turn on and off, thus eliminating the need to dispatch staff to a facility. The phone systems also allow for remote operation of the lights from any location.

Avoiding instances in which field lights are left on unnecessarily is one way to limit the system's negative impact on a neighborhood, but there are other creative solutions to controlling the amount of light a system generates. Alternate switching or dimming systems can be specified for fields that require higher levels of illumination for higher classes of play. Typically these systems only need to be operated at full output a small percentage of the time. Reducing the lighting levels during the majority of events hosted by the field reduces not only the amount of light cast into the surrounding community, but the facility's energy consumption, as well.

The tendency to over-illuminate fields that have minimal spectator requirements may be driven by a school or parks department's desire to install a best-case-scenario system that meets specifications for the highest possible levels of competition. According to the Illuminating Engineering Society of North America, Class IV specifications suitable to recreational football and soccer fields dictate an average maintained lighting level of 20 foot-candles. However, Class III and Class II specifications, which meet spectator requirements for high school competition, mandate lighting levels of 30 and 50 foot-candles, respectively.

A neighborhood soccer field may only be programmed for competitive recreational use and attended by 20 spectators at any given time; thus, Class IV specifications easily suffice. For a high school football stadium that seats fewer than 1,500 spectators, Class III specifications will meet minimum lighting requirements. Any additional (and unnecessary) lighting results in increased risk of light trespass, glare and sky glow.

Officials at Division III Lewis & Clark College in Portland, Ore., recently lighted their football stadium to hold Northwest Conference night games and local high school district playoff games. This required the field to be lighted at levels meeting Class II specifications, but for only eight events each year. (The city of Portland capped the number of nighttime events in the interest of limiting noise and traffic.) The remainder of the year, the synthetic-turf field is used for Pioneers team practices and student recreation. To address the multiuse nature of the facility, a control system was designed using alternating relays, with the option of turning on only half the floodlights on each pole at any given time to meet Class IV lighting requirements - all the while maintaining excellent lighting uniformity. Moreover, the system automatically switches from one half of the lights on each pole to the other half each successive time the lights are turned on at Class IV levels. This nearly doubles lamp life, resulting in less frequent lamp replacement and lower maintenance costs.

Lighting engineers must be sensitive to community needs and environmental concerns on every project. Field operators are expected to provide recreational opportunities with limited budgets, and the lighting of athletic fields helps them meet that goal. On the other hand, neighbors and naturalists want to protect their personal and community quality-of-life investments. No one looks forward to battles with these groups - but they are a possibility, perhaps even likely.

Addressing the balance of field usage and lighting impacts early on is critical to the overall success of a project. Lighting engineers who can demonstrate knowledge of and experience with the various types of available lighting equipment and the design strategies specific to athletic field lighting will go a long way toward minimizing public-relations fallout and - ultimately - the adverse effects of the finished product.