Eons ago the humans looked to the stars for geographical navigation and interpretation of time; and as centuries passed, human curiosity peaked in all aspects of astronomy. Much of the historical and present day literature, scientific research and philosophy have been based on the night sky and the astronomical wonders. The rotation of the earth around the sun causes the day and night cycles and variations in tides and seasons. The proverb “Make hay while the sun shines” aptly describes how, apart from nocturnal flora and fauna, all other life forms are active during sunlight hours (day) and inactive/ resting during the dark hours (night). More importantly, the day-night cycles are also responsible for the circadian rhythms and biological clock in nature.
In the last century, with developing technologies, human society has increased its exposure to artificial illumination, producing changes in the light/dark cycle, as well as in light wavelengths and intensities. Although, the consequences of unnatural illumination or light pollution have been underestimated by modern society in its lifestyle, light pollution may have a strong impact on the health of all life forms. The effects of artificial light sources could have direct consequences on retinal health, which may lead to dizziness, confusion, fatigue etc.
There are 5 types of light pollution: skyglow, glare, over-illumination, light trespass and light clutter. Skyglow is caused due to reflection of badly directed light escaping into the sky, which is then scattered by the atmosphere, giving the appearance of a glow. Glare is the direct exposure of the retina to the light source; there are 3 types of glare namely blinding, disability and discomfort glare, based on level of exposure and intensity. Over-illumination is the effect caused due to usage of intense light beams where lower intensity beams would suffice. Light trespass is caused by light falling onto neighboring property causing them discomfort. Light clutter is the effect caused due to the grouping of colorful lights with different intensities in an area. All these types of light pollution impact life forms in different ways and can constitute energy wastage, especially upward directed lighting at night. According to international reports, 50% of the light from a typical unshielded light fixture is wasted, shining upward where it is not needed. About 40% of the light shines downward to illu¬minate the intended target. Light emitted horizontally tends to create glare. Different light emitting structures such as globe lights typically distribute light poorly and contribute to glare. Flood¬lights can fill a space with light, but they may be too bright for their intended task, and much of the light is wasted. Such energy wastage is also a waste in cost and carbon footprint.
Figure 2: Directionality of the Light source
Many insects, birds, mammals and reptiles are photoperiodic in nature. Their life cycle depends heavily on the day & night cycle. Most affected, by light pollution, are nocturnal animals which evolved and adapted to the darkness, to better suit their needs. Birds, while migrating at night, collide with tall well lit buildings and immature birds suffer disproportionately. Bats exposed to artificial night lights tend to avoid lit areas for foraging or seed dispersal. Nocturnal birds like owls, kakapos and kiwis avoid lit areas, to avoid predation, and this causes an impact on their feeding and mating behavior causing a drastic decline in their numbers. Daytime foraging species tend to continue foraging even under artificial lights, causing competition, for food, with nocturnal fauna. This also impacts songbirds like blackbirds and nightingales which sing at unnatural hours, in the presence of artificial lights. Also, with the constant appearance of daytime, caused by the artificial lighting, the fauna are unable to keep track of the lapsed time and this causes a major impact on migratory species; since migration is a precisely timed biological behavior. This causes further impact on mating, feeding and species proliferation of migratory fauna. Many species of sea turtles lay their eggs on beaches, with females returning for decades to the beaches where they were born to nest. When these beaches are brightly lit at night, females may be discouraged from nesting in them; they can also be disoriented by lights and wander onto nearby roadways, where they risk being struck by vehicles. Light is one of the environmental cues that tell animals where to go and one of the major impacts of artificial lights, is seen on sea turtle hatchlings, who normally navigate towards the sea by orienting away from the elevated, dark silhouette of the landward horizon. In the presence of artificial lights, the hatchlings navigate towards the landward light source and never find the sea, eventually resulting in their death.
Firefly behavior has been observed to be affected by bright incandescent lights, since it mimics their spectrum of signaling. Fireflies typically won't make an appearance where there are bright ambient lights, such as full moon nights. They too are impacted, since their ability to signal each other is interrupted by the artificial lights, disrupting mating and leading to fewer fireflies being born each year.
Frogs have been found to inhibit their mating calls when they are exposed to excessive light at night, reducing their reproductive capacity. Lab studies show that the amount of light exposure affects DNA synthesis and the production of hormones—hormones that regulate everything from how much fat the frogs store for the winter to when they produce eggs. Many insects are drawn to light, but artificial lights can create a fatal attraction by increasing insect vulnerability to predation. Night time lights also impact the plants ability to generate the hormone, phytochrome. Abnormal levels of this photosensitive hormone can have consequences for a plant's flowering cycle, seed germination and dormancy.
A hormone, Melatonin, found in animals, plants, fungi and bacteria, anticipates the onset of darkness i.e melatonin is secreted by the cells during night/dark periods. In animals, melatonin is involved in the synchronization)of the circadian rhythms of physiological functions such as sleep timing, blood pressure regulation, seasonal reproduction and many others. The change in duration of secretion serves as a biological signal for the organization of daylength-dependent (photoperiodic) seasonal functions such as reproduction, behavior, coat growth and camouflage coloring in seasonal animals. Abnormalities in melatonin levels have often been linked to cancers in humans, although no conclusive evidence of this has been found yet. This does not mean there is no effect, but rather, there isn’t enough evidence to render any definitive conclusion at this time.
The outcomes of our bright new world are more readily noticed in less adaptable organisms living in and around the vicinity of our artificial-light glow. Living within a glare of our own making, we have cut ourselves off from our natural, evolutionary and cultural ancestral-endowments i.e. the light of the star studded night sky and the rhythms of day and night. Citizens of the globe are becoming more aware of the impacts of light pollution and many successful programs like ‘Earth Hour’ and ‘Lights Out’ are being adopted world-over. Unlike other environmental issues, light pollution can be solved, and with the constant developments in environment-friendly technology, it is an achievable goal.