Artificial Light at Night (ALAN), an Anthropogenic Pollutant: A Narrative Review

The simplest definition of light pollution (LP) is the presence of artificial light at night (ALAN) at inappropriate times, intensity, and inappropriate amounts and colors. All these parameters of anthropogenic light clearly indicate that the presence of ALAN can disrupt the proper functioning of not only humans but all organisms on Earth that have evolved in conditions of alternating day and night, closing within a 24 h day. Cities are the primary source of LP, and the ever-increasing global urbanization makes LP one of the fastest-growing threats to our civilization. It is particularly dangerous because public awareness of its existence is exceptionally weak, as the presence of light is usually perceived as a good thing, generating safety and beauty, and it is difficult for people to understand that excess of light may turn against us. However, LP dysregulates the well-known circadian rhythms of humans and animals and disrupts normal plant physiology. Furthermore, in a light-polluted world, plant–pollinator relationships are also endangered, which can lead to disruptions in food chains. In this review, we will present various aspects of excessive lighting and propose solutions to mitigate the increasing LP, considering the threats it poses to all living organisms.