NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 20 3.2.3 Too Little or Too Much Light Poorly designed lighting that results in inadequate lighting (too few lights, too low intensity, or inadequate coverage) or over-illumination (too many lights, too high intensity, or excessive coverage) poses a safety risk for humans. Lighting is needed for safety in certain situations, and too few lights, overly dim lights, or lights spaced too widely may result in poor illumination and accidents. However, over-illumination may also cause accidents because it negatively affects dark adaptation and can cause so much contrast that objects in less illuminated areas cannot be seen at all. Additionally, if the light source contrast is so great that glare occurs, over-illumination may cause visual discomfort or temporary visual impairment that causes viewers to look away or reduces their ability to see at all. Over-illumination may also present a personal security risk because high contrast between illuminated and nonilluminated areas may make it very difficult to see people in darker areas away from light sources (Kraus 2016). If too many lights are in view from a given location, the resulting light clutter may have aesthetic effects or even pose safety risks due to distraction, primarily of drivers, but also potentially of workers at a facility. These effects are more common in urban areas, due to massive over-illumination, but may occur on intensively developed BLM-managed lands, such as major oil and gas fields. 3.2.4 Light Trespassing Where It Is Not Wanted Light trespass is light where it is not wanted or needed (e.g., streetlights shining into bedroom windows at night, the synchronized flashing of lights on wind turbines). In other words, lighting is present in an area where little or no lighting is desired. The lighting does not have to be close by to cause an impact; as noted in Section 3.1.3, lights at night can be visible at distances exceeding 36 mi (58 km) (Sullivan et al. 2012). 3.3 Effects of Artificial Light at Night on Humans Research on the effects of light pollution on humans is a relatively new field but clearly shows that numerous effects are occurring. This section summarizes the major effects of light pollution on humans, including aesthetic, spiritual, and recreational effects; historic and cultural effects; astronomical and scientific effects; nuisance effects; human health effects; and economic effects. 3.3.1 Aesthetic, Spiritual, and Recreational Effects As discussed in Section 2.1, viewing dark night skies relatively free from light pollution is a highly valued aesthetic experience and, for many, a deeply spiritual experience. Dark night skies also contribute to the wilderness experience, which many people seek when they visit wilderness areas. Skyglow often diminishes the aesthetic, spiritual, and wilderness values of the night sky by making it Intensely bright lights at a remote natural gas facility in New Mexico. The synchronized lights on wind turbines are a source of light trespass that may be visible for many miles.
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