Published In March 2001
The next time you drive by an outdoor sports field, notice that each floodlight has a unique combination of rotation and tilt angles. This complicated array configuration, whereby individual floodlights illuminate a small portion of the playing surface, embodies the distinct challenges of sportslighting applications. However, considering five primary factors simplifies sportslighting: * unique characteristics of the playing surface; * type of lighting fixture; * lamp source and wattage; * pole location and mounting height; and * lighting level requirements. Field characteristics Most sports are played within predetermined boundaries. These include football, soccer, tennis, basketball, and hockey. In baseball and softball, however, the only constant is that the basepaths for first and third base are 90 degrees opposed to one another. All other dimensions are determined by the application. Depending on the classification of competition, the distance between the bases varies from 60 to 80 feet on a softball field, and from 60 to 90 feet on a baseball field. The outfield might be a symmetrical arc, a series of straight segments, a bulging arc, or some combination of line segments and arcs. Always take note of obstructions that might limit pole/fixture location (e.g., land contours, running tracks, or power lines). Whenever possible, obtain an engineered site plan, or at least a dimensioned sketch of the field, before designing the lighting system. Type of light fixture Choosing light fixtures requires special consideration. The two most common styles are decorative cut-off fixtures and symmetrical sportsfloods. Decorative cut-off or “shoebox” fixtures are typically used where the playing surface is relatively small and mounting heights are between 20 and 30 feet (e.g., outdoor tennis, volleyball, and basketball courts). Cut-off luminaires, which offer maximum light on the target surface while minimizing spill light, are also used when controlling light pollution is critical. Symmetrical sportsfloods are commonly used for large-area applications. Each floodlight consists of a spun aluminum reflector capable of producing a variety of beamspreads, which lets the designer illuminate large areas from a single pole location. Narrow beamspreads (National Electrical Manufacturers Association (NEMA) 2 & 3) allow light to be aimed at targets from 100 to 250 feet away, medium beamspreads (NEMA 4 & 5) from 50 feet to 150 feet away, and wide beamspreads (NEMA 6 & 7) from up to 100 feet away. The ballast for each sportsflood may be integrated in the fixture housing. To reduce weight on the pole top, groups of ballasts can also be installed in a remote enclosure low on the pole. Current computer software allows the designer to determine the location of each pole and aim multiple floodlights from each location. The software also records the required rotation and tilt of each floodlight, which is then used to generate an aiming diagram for system installers. Lamp source and wattage While a few smaller sports applications use incandescent lighting, most employ a high- intensity discharge (HID) light source. In an HID lamp, light is generated by igniting gas in an enclosed chamber known as an arc tube. The table below details the light- and color-producing properties of the most common HID light sources. A combination of high efficacy and good color rendition makes metal halide the most common light source for sports applications. Pole location and mounting height Pole location and mounting height often get the least attention, but can significantly affect a project’s final appearance. The most common design mistake involves mounting height, which should be determined by pole location, size of illumination area, and required light level. When sportsfloods are mounted too low, the designer must use flatter aiming angles to illuminate areas farthest from the pole, causing glare for athletes and spectators alike. Not only is glare a nuisance, but it can create a dangerous and litigious situation. Lighting level requirements In recent years, the industry has debated about the light level necessary to provide a safe playing environment for athletes. The Illuminating Engineering Society of North America (IESNA) has established guidelines concerning light levels for all sports, as reported in IESNA publication RP-6. Light levels for a sportslighting system are measured on an imaginary grid based on the size of the playing surface. Baseball and softball use independent calculation grids for the infield and the outfield. To address faster ball speeds, the infield typically has a higher light level, which allows for better reaction times. On any calculation grid, the point of brightest light is called the maximum (max) and the point of lowest light is called the minimum (min). The total of all calculated points, divided by the number of points, is called the average (avg). Light uniformity, represented by max/min and avg/min ratios, is equally important. Max/min represents the brightest point of light versus the lowest point of light on the calculation grid, while avg/min denotes the average versus the lowest point. The lower the ratio, the better the uniformity. To ensure a smooth and safe uniformity, the max/min ratio should not exceed 2:1. BOOKER is applications engineering manager for Thomas & Betts Corporation in Memphis, Tenn. He can be reached at keith_booker@TNB.com.