NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 56 5.4.2 Do Not Aim Lights Upward, Horizontally, or at Large Angles from the Ground Lights aimed into the night sky are a major source of skyglow. Lights that are aimed horizontally, or nearly so, produce more skyglow at long distances than lights aimed upward, because the light travels through a longer distance of atmosphere and thus encounters more scattering particles. Lights aimed at a large angle from vertical may also greatly increase light trespass and glare. It is recommended that luminaires meet the IES TM-15-20 BUG ratings (IES 2020) as installed for the applicable lighting zone performance standard (see Sections 5.1.2 and 5.4.5). Aiming lights downward (e.g., on drilling rigs) reduces light trespass, glare, and skyglow. It may also improve safety and security in over-lighted/glare situations and reduce shadowing. Notes: The “Luminaire Classification System for Outdoor Luminaires” (IES 2020) specifies the amount of light allowable in each zone for a given BUG rating, including high angle zones (front high, front very high, back high, and back very high zones), as shown in Figure 4 in Section 5.1.2. The amount of light emitted in each of these zones is often found in luminaire specifications. Aiming lights straight downward is impossible in some situations. Avoiding uplight does not ensure that sensitive habitats are protected from adverse impacts. Do not point lights downward into rivers, streams, wetlands, and other sensitive habitat areas. 5.4.3 Re-Aim Existing Lights to Illuminate Task Targets Existing lights may be improperly aimed, either without awareness or inadvertently. After careful consideration of lighting needs for an illuminated area, ensure lights are aimed properly to illuminate task targets. This may reduce light trespass and glare and may improve safety by providing better task lighting, as long as lights do not over-illuminate the target. Notes: Some lights cannot be re-aimed. Others can be re-aimed at the task area, but if the task area is too far from the light source, the light may point at a high angle from the ground surface, which could increase skyglow, light trespass, and glare. 5.4.4 Use Dark Sky-Compliant Luminaires Use dark sky-compliant luminaires or luminaires designed to reduce environmental effects. A properly designed and installed lighting fixture that follows the six guiding principles provided in Section 4 is considered dark sky friendly. These horizontally aimed floodlights cause skyglow, light trespass, and glare. Downward directed lights reduce skyglow, light trespass, and glare.
RkJQdWJsaXNoZXIy NTkzMzk=