NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 17 3.1.3 How Distance Affects Light Pollution Multiple types of light pollution may occur simultaneously in a given setting. The types of light pollution differ in many respects, including the magnitude of their effects at varying distances. Relatively little field-based research exists to address the question of distance related to light pollution and measured effects. It is known that some effects of light pollution are of ecological importance even at relatively short distances. For example, effects on crop plants occur within tens of meters of a light source (Sinnadurai 1981), and photosynthesis induced by artificial light at night is thought to occur when vegetation is within inches of a light source (Gaston et al. 2013). Light pollution may affect animal behavior from far greater distances. For example, Van Doren et al. (2017) observed bird attraction to sources of light in the dark as far as 4 km. No available studies have calculated the distances that glare (which is a subjective effect that varies from viewer to viewer) is troublesome to humans at night. Glare from reflected sunlight in the daytime can cause discomfort at distances exceeding 20 mi (32 km) (Sullivan and Abplanalp 2015). The distance at which light trespass, light clutter, or over-illumination is noticeable is limited only by the maximum distance at which the associated light sources themselves or their reflections from the ground, structures, or water bodies are directly visible. Sullivan et al. (2012) observed nighttime wind turbine lighting at more than 36 mi (58 km), and it is likely that brighter lights are visible at substantially greater distances, though the distance may not be as great in areas with high humidity or poor air quality. Sullivan and Abplanalp (2017) observed night lighting at a solar facility on BLM-managed lands at 29 mi (47 km). Skyglow may be visible at very long distances. Skyglow from Las Vegas is sometimes plainly visible from within Death Valley National Park, at more than 100 mi (161 km). The relatively long distances at which some types of light pollution are noticeable is important to consider in the context of BLM-managed lands. Light pollution from sources miles away can affect resources and people on BLM lands, and in the case of skyglow, the effects can be noticeable even when there is no direct line-of-sight from the offending light sources. Similarly, light from facilities and activities on BLM-managed lands can affect people and animals many miles away from BLM lands. Addressing light pollution requires cooperation between the BLM and its neighbors. For example, the BLM is a member of the Colorado Plateau Dark Sky Cooperative, an organization that links local, state, and federal agencies; tribes; businesses; nonprofits; educational institutions; and local communities in a collaborative effort to protect night sky values by minimizing the effects of light pollution (Colorado Plateau Dark Sky Cooperative 2018). Lighting at this solar facility on BLM-managed lands in Nevada as seen at 15 mi (24 km). The foreground lights are from vehicles traveling on Interstate 15.
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