Nightfall keeps the circadian rhythm of plants and animals in synchrony with their natural activity and the environment. For humans, the threshold for the blue light of twilight is roughly a few times the brightness of the full Moon and somewhat less for some other species. Altering the night's brightness and its spectrum changes the natural cues for the onset of night that will shift or delay the biological benefits of night by changing or disabling some aspects of the organism's biochemistry. There have been many diverse studies into the impact of artificial (anthropogenic) light at night (ALAN) on various aspects of wildlife. These highlight the dependence on the extent and brightness of the light and its spectrum. Scheduling or timing the use of light is the fourth attribute that has a profound impact on the biology of the night (Navara and Nelson 2007), but the timing of ALAN need not be exact. Animals have a natural plasticity in their behaviour and biochemistry that can tolerate some shifts in the natural time of night (Reebs 2002, Wong 2015). This can be used to determine a schedule for outdoor lighting that will reduce its impact on the ecology, yet will accommodate human activity.
展开▼
