Let the light lead to growth for all

    28-Jan-2020
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. 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. Today around a quarter of the Earth's surface is polluted by ALAN originating from industry, residential areas and transportation networks.  India has also witnessed a remarkable change from low to high light pollution. Urban expansion, industrial development and air pollution are main drivers for increasing light pollution.
Upon devising light bulb in September 1878 technology for the world's first 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 infinite”. It is true because recent satellite data estimates over 80% of the world's human population experiences artificial 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 benefits 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 extraterrestrial 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 population 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. 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.
The widespread introduction of high intensity white LEDs, which are cheap, bright, highly efficient 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 significant 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 population 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.
To be contd