NIGHT SKY AND DARK ENVIRONMENTS: BEST MANAGEMENT PRACTICES FOR ARTIFICIAL LIGHT AT NIGHT ON BLM-MANAGED LANDS TECHNICAL NOTE 457 23 3.3.5 Human Health Effects Humans have circadian rhythms, sometimes referred to as “biological clocks5,” that have developed in response to the earth’s day-night cycle, and among other things, they set the human sleeping and waking cycle. Exposure to artificial light at night can interfere with and suppress melatonin6 production, affecting human health and sleep. (Tähkämö et al. 2019). Light timing and wavelength are important with respect to circadian disruption and the suppression of melatonin secretion. Melatonin suppression peaks at light wavelengths around 480 nanometers. Melatonin suppression is especially sensitive to shorter light wavelengths in the evening, with cooler colored (bluer) light suppressing melatonin production more than warmer (redder) light (Tähkämö et al. 2019). For this reason, it is important to use warmer light colors regardless of lighting type to minimize health effects to both humans and animals (see Sections 3.4 and 3.5 for discussion of health effects in animals). Evidence suggests direct and indirect links between exposure to artificial light and melatonin suppression that may result in various medical problems in humans, including increased risk of obesity, heart disease, and various types of cancers (Hurley et al. 2014; Kloog et al. 2009; McFadden et al. 2014). It is important to note that humans typically get most of their nighttime light exposure in indoor spaces, not outdoors, and consequently, much of the research into human health effects has examined indoor effects of lighting. 3.3.6 Economic Effects The night sky and darkness are often not considered in terms of economic benefits; however, there are positive economic effects of dark night skies. It is also clear that light pollution can have negative economic effects. 5 Technically, circadian rhythms and biological clocks are not the same. Circadian rhythms are physical, mental, and behavioral changes following a daily cycle, determined by an organism’s biological clocks but affected by environmental factors, including light and darkness in the organism’s environment. Biological clocks are an organism’s innate timing device, composed of proteins that interact in cells in nearly every tissue and organ (NIH 2017). 6 Melatonin is a hormone that, among other important functions, affects circadian rhythms, sleep and wakefulness, and biological repair mechanisms. Expenditures associated with nighttime recreation on public lands can in some instances be estimated. For example, astrotourism is associated with economic activity in nearby communities, as many participants require overnight stays (Collison and Poe 2013). A study conducted for the National Park Service by Mitchell and Gallaway (2019) conservatively estimates astrotourism-related spending in national parks in the Colorado Plateau alone at $5.75 billion for the 10-year period between 2015 and 2024. To the extent that light pollution prevents or discourages astrotourism and other nighttime recreation activities, related economic activity is reduced. The effects of light pollution have caused some major observatories to be rendered useless for the types of astronomical work for which they were intended, and it is now common practice to build new observatories in extremely remote locations, at great additional cost (Luginbuhl et al. 2009; Henderson 2010). Stargazing opportunities are growing in popularity and demand. Locations and facilities that support astrotourism are increasing like this observatory deck at the Lowell Observatory located in Flagstaff, Arizona. The city is actively working to limit light pollution in recognition of the growing importance to local tourism.
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