NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 36 The purpose of the second guiding principle is to use adaptive lighting controls and temporary portable lighting sources to provide lighting only at the time the lighting is needed. Adaptive controls are electronic or mechanical devices attached to a light to dynamically control the duration, intensity, spectrum, or area illuminated by the lighting. Use of adaptive controls and temporary lighting in most cases substantially reduces the amount of time lights are in use, effectively eliminating the source of light pollution and related effects while also saving energy and money, both through reduced energy costs and extended life of the light sources. A variety of adaptive controls, such as motion sensors, photo sensors, timers, and dimmers, are available to limit lighting to specified periods when the lighting is needed or to turn lighting on automatically when triggered by the presence of humans. Dim lighting during periods of low human activity. Use lighting controls to turn lights off after business hours, when they are seldom needed. In the absence of automated controls, simply turning lights on only when needed and turning them off when no longer needed is effective and costs nothing. An aircraft detection lighting system (ADLS) is a type of adaptive lighting control for structures taller than 200 ft, including wind turbines, communication towers, and certain electric transmission towers. ADLSs provide radar surveillance of the airspace around these structures and automatically issue signals to activate obstruction lighting when aircraft are detected at a specified distance. 4.3 Light Only Where Needed: Shield Lights and Direct Them Properly The purpose of the third guiding principle is to direct light only where it is needed, and not elsewhere, by focusing light only on intended surfaces using properly shielded luminaires and, where feasible, other methods, to screen the light from viewers. Using unshielded or partially shielded lights and pointing lights upward, horizontally, at high angles below horizontal, or even downward into rivers, streams, wetlands, and other habitats increases light pollution and may have harmful ecological effects. Wherever possible, use fully shielded luminaires, with additional side shielding. Fully shielded luminaires emit no uplight (i.e., no light is emitted above 90° from horizontal). “Fully shielded” is analogous to a BUG uplight (U) rating of “0” (IES 2020) (see Section 5.1.2 for a description of the IES TM-15-20 BUG rating system). Consider directing luminaries only at the surfaces requiring illumination (e.g., for task performance) and from an appropriate height to provide the coverage needed without illuminating an unnecessarily large area. These practices limit direct visibility of the light source and the amount of reflected light from the illuminated surface. Additionally, where feasible, place lights so that structures screen the light source or cast light from view. 4.4 Light Color Matters: Select Amber, Orange, or Red Whenever Possible The purpose of the fourth guiding principle is to use light colors that are less disruptive. Warm light colors, such as amber, orange, and red, use longer wavelengths that are less disruptive to humans and wildlife (e.g., melatonin production, dark-adapted vision) and, in general, are dark sky friendly (e.g., less skyglow). As discussed in Section 3.1.1, blue-rich light (> 3,000 K) generally has greater potential for negative effects than “warmer” color light (< 3,000 K), such as amber or red light. Blue light has the greatest potential for interfering with melatonin production. Insects are preferentially attracted to blue-rich light sources, which can affect development, survival, and reproduction in some insect species. Blue-rich light has a greater effect on skyglow and is more likely to cause disability glare than warmer color light. Shorter wavelength light also degrades scotopic vision more than longer wavelength light because the photoreceptors in the eye that are dominant in scotopic vision (the rods) are more sensitive to shorter wavelength light (Motta 2018).
RkJQdWJsaXNoZXIy NTkzMzk=