Sunday, Jan 12, 2020 13:45 [IST]
Last Update: Sunday, Jan 12, 2020 08:14 [IST]
Lights: not necessarily positive
Dr DEBAPRIYA MUKHERJEE
My frequent visit to native village named Moutorh in Purulia district (West Bengal) to promote science education through practical demonstration among the students from V to IX had experienced the problem of pain in the eye among some students while reading continuously for 3-4 hours at night. On enquiry from their parents I came to know that it would be a great excuse not to read but to play with mobile game. But the way students were stating the fact convinced that it was real as I had little experience on the impact of artificial light at night (ALAN). Light pollution may be the cause of this suffering.
Another incident can be stated that there is not a single crow in my village. Further probing I realized that ALAN particularly during marriage and other social functions as well as cutting the trees forced the crow leaving the places as they were living closed to the village houses. Along with crow, population of other birds and insects are severely declined. Many old people in this villager has agreed that this evidence that light pollution has profound and serious impacts on ecosystems particularly in declining the population of birds and insects as well as on human, is overwhelmingly strong even in this rural area. Today around a quarter of the Earth's surface is polluted by ALAN originating from industry, residential areas and transportation networks. In India, New Delhi, Telangana, Maharashtra, Karnataka and Uttar Pradesh experienced increase in very high light pollution intensity. West Bengal, Gujarat and Tamil Nadu witnessed a remarkable change from low to high light pollution. Urban expansion, industrial development and air pollution are main drivers for increasing light pollution. The increase in ALAN merits immediate attention to create awareness among the people. Now it is a global concern but the pattern of ALAN pollution inside urban areas has not yet been fully explored.
Upon devising light bulb in September 1878 technology for the world's ?rst mass-produced electric lighting system, Thomas Edison wrote in his laboratory notes: “With the process I have just discovered, I can produce a thousand – aye, ten thousand – from one machine. Indeed, the number may be said to be in?nite”. It is true because recent satellite data estimates over 80% of the world's human population experiences arti?cial light at night, with both the extent and brightness of lit areas increasing at a rate of 2.2% per year between 2012 and 2016. Arguably, the light bulb is the most transformative invention humans have introduced to this planet. Working hour have remarkably increased both in office and home. Now, we work long after the sun sinks below the horizon. We more safely roam city streets after dark. Obviously ALAN has some clear bene?ts for humankind, such as increasing opportunities for economically productive activities, leisure and recreational activities. But light bulbs have a dark side because they have stolen the night. The vast majority are unable to experience the natural wonder of a truly dark sky , blanketed with stars.
Light in nature mainly originates from extra-terrestrial sources, such as the sun, moon, and stars, or emission from the upper atmosphere like airglow or aurora. The illuminance (measured in “Lux” i.e “lx”) that reaches on Earth’s surface is a maximum of about 120,000 lx during the day and decreases to about 800 lx at sunset. At night, the maximum illuminance reaches about 0.3 lx on a full-moon night, which decreases to about 0.001 lx on a moonless clear night and even further for cloudy condition. In urban areas, direct ALAN can reach light levels up to 150 lx, which is 1000-fold brighter than a clear full-moon night and of markedly different spectral signature than natural light. Indirect light pollution originating from light is scattered within the atmosphere and occurs as skyglow that is visible over large distances. 80% of the world population and >99% of populations in the united States of America (USA) and Europe live under light-polluted skies. Skyglow changes with atmospheric and weather conditions, potentially resulting in night-sky brightness (luminance) levels hundreds of times brighter than natural, and surface illuminance levels brighter than a full moon. Skyglow can also mask the blue peak present during twilight which plays an important role in the circadian entrainment. The spectral composition of skyglow depends on the type of lamps used for ALAN. In some extremely light polluted places the sky is so filled with light that 99.5 percent of all stars are completely invisible without optical aid. Though many places of Earth remains free of direct artificial light, but skyglow is more widespread and tends to reduce the contrast of the night sky which makes it harder for astronomers to view the heavenly bodies.
According to researchers, skyglow may threaten 30% of vertebrates and 60% of invertebrates that are nocturnal and exquisitely sensitive to light because the level is well above the thresholds for triggering many biological responses. The inexpensive white light-emitting diodes (LEDs) often found in street lights emit wavelengths of blue light that bounce around in the atmosphere, potentially increasing sky glow.
The widespread introduction of high intensity white LEDs, which are cheap, bright, highly ef?cient and low energy consumption but exacerbates the problem due to light emissions with “bluer” and more polluting light spectra compared to more yellow light emitted by previous lighting technologies, such as incandescent and low pressure sodium lights. Most importantly, LEDs are rapidly becoming one of the world's most important light sources and are increasingly being used for lighting in both residential and commercial areas as well as the transport routes between them and thereby more short wavelength (commonly called blue) light, is introduced into the night environment and simultaneously this ALAN is endangering ecosystems by harming animals whose life cycles depend on dark.
The possible reason for not feeling sleepy as reported by the students is suppression of the production of melatonin because of exposure to excessive ALAN, though this problem was faced by only few students. The melatonin is responsible for unleashing a cascade of reactions that regulates sleep-wake cycles, lowers body temperature, slows metabolism, and increases leptin, a hormone that reduces appetite that reduces our hunger at night. The melatonin normally begins rising at sundown and peaks around midnight. Low melatonin levels due to exposure to electric light (computer/mobile screen indoor or outdoor) and circadian disruption also play a role in heart disease, diabetes, depression, and cancer—particularly breast cancer. Glare from outdoor lighting decreases our vision and increases chances of accidents at light.
Light pollution has a signi?cant impact on the organismal functions of birds, insects and other animals because it disrupts their internal clock and circadian rhythm even at the intensity of 0.05lx. According to the scientists, the melatonin levels in birds decreases with the increase of ALAN intensity and causes sleep deprivation and stress response in birds and therefore change their rest patterns. Many migratory birds while flying at night, light from the stars and Moon helps them to navigate. These birds are disoriented by the glare of artificial light while flying over urban and suburban areas. The American Bird Conservatory estimated that more than four million migratory birds perish each year in the United States by colliding with brightly illuminated towers and buildings. Light pollution also causes dramatic decline of certain migratory songbird populations over the past several decades Lights are well known to disorient migration of sea turtles. Among other navigational aids, sea turtles hatch at dark and hatchlings use moonlight over the water to return to the ocean. For example, sea turtles hatch when its dark and the hatchlings use the light over the water to return to the ocean. Light from the buildings on the beaches draws hatchlings away from the water. But bright ALAN originating from high rises, resorts, bars, malls, restaurants, and homes along the coastlines create countless false moons and alluringly bright horizons, and the tiny turtles get disoriented and wander into roads in huge numbers. For a hatchling, each minute on land means dodging an array of winged, wheeled, and walking dangers. When the sun comes up, a disoriented, land-locked turtle is almost literally toast—dehydrated, overheated, and easy pickings for predators. As a result, millions of sea turtles die every year in Florida. Light pollution can also meddle with aquatic life in lakes. Zooplankton normally dwell deep below the water in the day and ascend to the surface at night to feed on algae. But ALAN impedes zooplanktons from consuming surface algae which leads to algal blooms that may disrupt plant life and lower the water quality.
Habitats that are exposed to increased ALAN due to anthropogenic activities face a variety of other manmade abiotic stressors including noise, chemical contamination, or other effects related to changes in land use practices. ALAN—in combination with habitat loss, chemical pollution, invasive species, and climate change—is driving insect declines. An estimate of the effects of street lamps in Germany suggested that the light could wipe out more than 60 billion insects over a single summer. Street lighting prevents moths pollinating as they end up flying into glare instead, exhausting themselves and leaving them vulnerable to predators. Therefore there is urgent need to put emphasis on the importance of keeping any disruption to natural system to an absolute minimum.
Many studies have been carried out to evaluate adverse impact of ALAN on individual species, the whole ecosystems and the services many species provide, such as crop pollination and also response of plant and animal communities to both direct light and the skyglow. Ecologists all over the world face challenges such as measuring light accurately and assessing how multiple species behave in response. But early results suggest that light at night is exerting pervasive, long-term stress on ecosystems, from coasts to farmland to urban waterways, many of which are already suffering from other, more well-known forms of pollution. But still the study that has been carried out to address the climate change, has not been done so extensively for clear understanding of light pollution and its impact on whole ecosystem. As said by Steve Long, a plant biologist at the University of Illinois at Urbana–Champaign and editor of the journal Global Change Biology. “We’re gambling with our future in what we’re doing to the environment.”
Best Solutions to pollution include turning off unnecessary lights to save money and environment and putting shields on streetlights to direct beams downward to prevent skyglow. Keeping the lights off between midnight and dawn is enough to prevent the disturbance to animal behavior that they trigger. For this, appropriate management strategy is needed to reduce the level of light pollution. Awareness about the health and environmental impacts of light pollution among communities can also be signi?cant for curbing this problem especially in case of developing countries like India. Adequate understanding of light pollution and holistic approach involving stakeholder and community participation is necessary to minimize its consequences. Regulation of light consumption in core urban areas simply to upgrade the visual look can also be reduced by implementing laws to maintain the minimum level of light consumption.