In humans (and many other vertebrates), ALAN suppresses production of the hormone melatonin, which plays a crucial role in regulating circadian rhythms, and which has been shown to be an aid to the immune system that helps suppress malignant tumour growth. Melatonin is most strongly suppressed by blue light, and excessively bright blue light can also cause retinal damage.
Epidemiological studies show strong correlation between ALAN and elevated rates of some hormonal cancers, obesity, diabetes, depression, and disruption of sleep. There is wide variation in sensitivity to ALAN among individuals, and safe dosage thresholds are not yet clearly established. While both indoor and outdoor lighting at night affects humans and wildlife, in this report we restrict our recommendations and discussion to the effects of outdoor light only.
Glare from poorly shielded or improperly installed outdoor lighting also poses a direct hazard to drivers, bicyclists, pedestrians, and other road users by
temporarily impairing their vision, especially for the elderly.
Many species of flora and fauna are negatively affected by ALAN. Approximately 30% of all vertebrates, including more than 60% of all known mammals, and over 60% of all invertebrates known today are nocturnal. A naturally dark night is an essential feature of their natural ecosystem.
ALAN can have significant effects on organisms and reduce the resilience of populations. Some organisms will avoid lit areas, while a few might benefit from the presence of ALAN, which has consequences on food-webs and habitat use. The impact of ALAN on the nocturnal organism level can cascade into ecosystems and can also affect day-active organisms and their ecological functions. ALAN impacts migration and habitat use, ecological functions, the timing and quantity of reproduction, and the immune system in various taxa. The impact of ALAN is a
major risk factor for biodiversity and consequently global food supply. The impact threatens many endangered nocturnal taxon groups such as bats and amphibians, but it also threatens the habitat and ecological functions for non-endangered organisms.
The impacts of ALAN are correlated with geographical features such as cities, highways and industrial sites, but the impact of ALAN as a pollutant is not limited by national borders. Skyglow, the brightening of the night sky caused by ALAN scattered within the atmosphere, results in elevated skyglow levels hundreds of kilometers away from cities and towns, where it can negatively impact ecosystems in otherwise remote and unlit natural areas. The WorkingGroup on the BioEnvironment compiled 13 recommendations to mitigate the
impacts of ALAN on humans, flora, and fauna:
|Title of host publication||On-line Workshop Dark and Quiet Skies for Science and Society Report and Recommendations|
|Publication status||Published - Nov 2020|