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Light Pollution is also known as photo pollution or luminous pollution.Itcan be observed as the brightening of a night sky due to scattering of artificial light by gaseous molecules and dust particles. It is a very little-known and less understood form of pollution and is only recently being recognized as a severe environmental and health hazard. There are five main categories of light pollution: light trespass, over-illumination, glare, clutter and sky glow[1].Light trespass occurs when unwanted light enters in a house from the outside, over-illumination is caused by intense lighting pointing upwards, glare is caused by vehicular lights, clutteris noticeable on roads where streetlights are badly designed or where brightly-lit hoardings line the roads and sky glow refers to the diffused glow that can be seen in over-populated areas[2].Light pollution is gradually encroaching upon more of the Earth’s surface with the annual growth of 2.2%, including newly lit areas. All living organisms have evolved with natural darkness of night over millions of years, which has been effected very badly with artificial lights at night. This artificial lighting levels in our cities are hundreds of thousands of times higher than the natural lighting levels due to starlight. The natural dark-light cycle is completely upset and impacting human life. The intensity and wavelength are two important parameters of light that affects the human eyes.

In the photometry, Lux is used as a measure of the intensity of light, as perceived by the human eye that hits or passes through a surface. Quantitatively the Lux is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area, equal to one lumen per square meter. The safe limit for direct exposing the light at human eyeis 50-60 Lux.As per a recent international study led by physicist Christopher Kyba from the GFZ German Research Centre for Geoscience in Germany, the artificially-lit surface of the planet at night increased in radiance and extent by 2.2% per year between 2012 and 2016[3]. Around this time, artificially-lit areas at night across India increased by 33%, a rise of 7.4% per year, more than three times the global growth [4]. Recent studies provide key insights into how the night sky has consistently gotten brighter across the world and New World Atlas of Artificial Sky Brightness is created by researchers. The atlas showed that 99% of the population of the US and Europe lives in places where man-made lighting erases the view of the night sky. Around 80% of land area on earth suffers from light pollution, which can adversely affect sleep cycles and the ability to see in the dark. Around 94% of Indians live under light-polluted skies, as many as 20% people in the world can’t see the Milky Way and 6% have night skies so polluted that rod cells (night-vision detectors) aren’t activated when looking at the night sky. Astronomers are particularly concerned with sky glow pollution as it reduces their ability to view celestial objects.Studies have been made to assess the awareness among Indians between the ages of 16–65 through an online questionnaire and it was found that majority of the participants were not aware about the term ‘light pollution’ and consequently were not aware about the threat that comes with it [5].So the objective of this study is to make people aware about the severity of the issue of light pollution and its consequences on our lives. 

A Threat to Human Health

In case of air and water pollution, the adverse effects on human health are immediately visible and could even be life-threateningbut light pollution has subtle and long-term effects on health. Medical research on the effects of excessive light on the human body suggests that a variety of adverse health effects may be caused by light pollution or excessive light exposure [6]. The circadian clock regulates physiologic activities such as brain wave patterns, hormone production, and cell regulation. The rhythms respond to the light and darkness for an organism. Disrupting these rhythms can result in a variety of health problems, including sleep disorders, anxiety, depression, diabetes, cancer (particularly breast and prostate cancer), cardiovascular disease, immunological disorders, and obesity, increased headache incidence, fatigue, stress and can elevate blood pressure [7]. We need good sleep in total darkness to reset our diurnal rhythm just as we need natural sunlight to reset our biological clocks. Light during darkness is a serious threat, not only to human being but to other organisms as well. Animal studies expressed that the disruption of the circadian rhythm is responsible for depression, weight gain, impulsivity and slower thinking.Ophthalmologists also warned about the perils of excessive light.

Light also affect the body’s inner clock. A deep sleep is very important for physical and mental health of human being, metabolic control of the body,working of human body systems(digestive, respiratory, cardiovascular)and also for cognitive or behavioralabilitiesof the human.Many studies point towards an increased risk of breast cancer and prostate cancer because of exposure to artificial light.Light pollution leads to hallucination, false orientation, sleep disorders,dry eyes, irritability and watery eyes. Light pollution has a wide range of negative effects on human health due to disrupting melatonin levels in the body.The level of melatonin is typically high during night in comparison to the day and its secretion is severely disrupted by even low levels of light. Reduction or elimination of light at night can help maintain a robust melatonin rhythm. Melatonin, the naturally occurring hormone that regulates the sleep and wake cycle, is acutely affected by light pollution. Melatonin disorders and disrupts circadian rhythms in human body because it is activated by darkness. The exposure of light at night suppresses the production of this hormone. Melatonin deficiency can result in anxiety and mood disorders, insomnia, and elevated estrogen/progesterone ratio.

Recent animal studies have identified the role of melatonin in suppressing cancer cells. The melatonin is suppressed by late night use of smart phones and laptops. Blue spectrum of light emitted by the LED screens of these electronic devices is the worst kind of light pollution.Blue spectrum light affects the photosensitive ganglion cells in our retinas. Photosensitive ganglion cells inhibit thefunctioning of pineal gland, which is responsible for melatonin production. Light pollution is not only a problem to human beings but it also affects flora and fauna very badly. Life exists with natural patterns of light and dark, so disruption of those patterns influences many aspects of animal behavior [8]. 

Light pollution aggravates air pollution also.Photochemical smog produces due to the chemical reactions of light, nitrogen oxides and volatile organic compounds in the atmosphere, which leaves airborne particles and ground-level ozone [9]. The presence of excessive light at night significantly slow down the nightly cleansing of environment, and enhance the Photochemical smog production.

Energy consumptions and energy production are the important aspect regarding development and danger of the planet Earth. Lightening is responsible for one-fourth of all energy consumptions worldwide. Lighting that emits too much light or shines when and where it’s not needed is wasteful. Wasting energy has huge economic and environmental consequences. Wasted light results in energy waste. According to a study estimated that 30% of all light emitted by public outdoor light fixtures is wasted, mostly by lights that aren’t shielded, which amounts to 22 Terawatt Hours (TWh)/year of wasted electrical energy. This is equivalent to the following: About 3.6 million tons of coal per year, about 12.9 million barrels of oil per year or the release of 21 million tons of carbon dioxide per year. To offset all that carbon dioxide, we’d have to plant 875 million trees annually. Public lightening is the single largest source of greenhouse gas emissions. The total amount of wasted electrical energy each year is enough to illuminate over 11 million homes per year and power over 777,000 [1].

Measures to Reduce Light Pollution

There is a global movement to reduce light pollution and there are several organizations working on it. One of these is the U.S.-based International Dark Sky Association (IDA), formed in 1988 to preserve the natural night sky. The purpose of IDA is to educate the public and certify parks and other places that have worked to reduce their light emissions. The first U.S. dark sky reserve was approved by IDA in 2017. The massive Central Idaho Dark Sky Reserve, which clocks in at 3,667 square kilometers (1,416 square miles), joined eleven other dark sky reserves established around the world. Up to December 2018, IDA has listed thirteen dark sky reserves on their site.As of January 2022, there are 195 certified Dark Sky Places in the world [10].

People are asked to action to reduce light pollution and bring back the natural night sky. Many states have adopted legislation to control outdoor lighting, and manufacturers have designed and produced high-efficiency light sources that save energy and reduce light pollution.Individuals are urged to use outdoor lighting only when and where it is needed, to make sure outdoor lights are properly shielded and directing light down instead of up into the sky, and to close window blinds, shades, and curtains at night to keep light inside, to use red light since light in the red spectrum does not suppress melatonin, to keep tech items (laptops, televisions, smartphones) out of your bedroom, and to use light sources of minimum intensity sufficient to accomplish the light’s purpose.

1. Southwest Florida Astronomical Society SWFAS old News letter’s “The Eyepiece May 2014” pp 7-11. 2. RasnaRajkhowa (2014), Light Pollution and Impact of Light Pollution, International Journal of Science and Research (IJSR), Volume 3 Issue 10, October 2014, p 861-867. 3. Christopher C. M. Kyba, TheresKuester, Alejandro Sánchez de Miguel, Kimberly Baugh, Andreas Jechow, Franz Hölker, Jonathan Bennie, Christopher D. Elvidge, Kevin J. Gaston and Luis Guanter (2017), Artificially lit surface of Earth at night increasing in radiance and extent,Science Advances, 22 Nov 2017:Vol. 3 (11). 4. “India Is Losing Its Night To Light, At 3 Times World Average”, CharuBahri, India Spend, 3 Dec 2017. 5. KomalKaushik, Soumya Nair, ArifAhamad, Studying light pollution as an emerging environmental concern in India, Journal of Urban Management, Volume 11, Issue 3, September 2022, P 392-405. 6. Gary Steffy, Architectural Lighting Design, John Wiley and Sons (2001) ISBN 0-471-38638-3. 7. Igor Knez, Effects of colour of light on nonvisual psychological processes, Journal of Environmental Psychology, Volume 21, Issue 2, June 2001, Pages 201-208. 8. T.Longcore and C. Rich, "Ecological light pollution". Frontiers in Ecology and the Environment (2004), 2(4): p 191–198. 9. Gardner, Sarah. "LA Smog: the battle against air pollution". Marketplace.org, American Public Media, 14 July 2014. Retrieved 6 November 2015. 10. International Dark Sky Association, https://www.darksky.org/