Minimizing Light Pollution: A Checklist for Action
Avoid outdoor lighting. Avoid outdoor lighting where it isn’t needed—but don’t sacrifice nighttime safety or the perception of safety. With schools and other facilities where vandalism is a problem, experiment with eliminating all lighting between 11 p.m. and 5 a.m. Use timers. Where acceptable, use timers to turn outdoor lights off during those hours when they are not needed (e.g., in parking lots after stores close and employees have left). Use motion-detector controls. For security applications, especially around residential buildings, specify motion-sensing controls so that lights will turn on when somebody walks by. Infrared sensors are recommended over ultrasonic sensors for outdoor lighting. Rapid-start lamps (typically fluorescent or incandescent) are required where motion-sensing controls are used. Turn off interior lighting at night. Design interior lighting in commercial buildings to switch off automatically when spaces are not occupied or after work hours. Consider occupancy sensors for residential buildings if lights are commonly left on by mistake. Minimize outdoor lighting levels. Carefully match outdoor lighting levels with the application and use no more than absolutely necessary. IESNA-recommended light levels are as follows (indicated in footcandles): Commercial building entrances (active): 5 Commercial building entrances (inactive): 1 General human safety: 0.5 – 5 (depending on hazards and activity level) Parking/pedestrian area: min. 0.2 – 0.9 (average to minimum ratio of 4:1) Pathways, outdoor steps: 1 Service station (pump island): 20 – 30 Specify “full-cutoff” luminaires. Specify outdoor light fixtures (luminaires) that are “full-cutoff” to avoid uplight or glare. Note that these are different from “cutoff” luminaires, which, as defined by IESNA, still allow some uplight. Several manufacturers of full-cutoff luminaires are listed at the end of the article. Avoid the use of floodlights. Keep lighting poles low and space more closely. For more uniform area lighting, such as parking lots, use a larger number of lower, pole-mounted luminaires instead of fewer, taller fixtures. Keep wattage below 250 watts. Focus light downward. Outdoor lighting fixtures should focus light downward. Even full-cutoff fixtures can contribute to light pollution if they are not properly aimed. A good rule of thumb is to make sure that direct light shines a minimum of 20° below a horizontal plane and in no case above the horizontal plane. Avoid uplighting. Wherever possible, avoid uplighting of trees and architectural facades. Lighting buildings from above, however, can be an important component of security lighting because it improves visibility on the streets and sidewalks below. Test installations for glare. After installation, check to make sure that glare will not be a problem for neighbors, pedestrians, or motorists. If glare becomes evident, modify equipment or design. Specify low-pressure sodium lamps near observatories. In applications where blocking light pollution is absolutely critical, specify low-pressure sodium lamps. These have the highest effi-cacy (lumens per watt) and their yellow, monochromatic light output has relatively low impact on astronomical observation. Avoid mercury vapor lamps. Mercury vapor lamps are very common for streetlights and general outdoor lighting, but high-quality, full-cutoff luminaires are often not available for these lamps. Mercury vapor lamps also have relatively low efficacy. Metal halide or high-pressure sodium lamps are preferable for most applications. Specify white light with good color rendering. For occupied spaces, specify energy-efficient lamps that produce relatively white light with high color rendering index (CRI). Putting quality light only where it is needed may enable less total light to be used. Illuminate signs from above. Advertising signs and billboards should be illuminated from above only—not from below. Illuminating signs from below results in significant waste when the light beam overshoots or has a larger diameter than the sign being illuminated, and upward-reflected light bouncing off of a sign contributes to sky glow. Avoid reflective surfaces beneath downlit signs. Whenever possible, design the surfaces beneath downlit signs to be light-absorptive rather than reflective. Landscape beneath signs with turf, for example, which has one of the lowest reflectivities of any ground surface. Strengthen light pollution regulations. Work with local planning commissions, planning agencies, or municipal governments to establish or strengthen regulations that will help reduce light pollution. A few strong voices can make a huge difference! Even a letter to the editor in the local paper or a phone call to an elected municipal official can bring about considerable change.
