How Light Pollution Harms Health Across India

On clinical evaluation, Kotwal--a retired lieutenant general in the Indian Army and president of the Endocrine Society of India--noted that the patient was overweight, and exhibited features suggestive of insulin resistance--skin tags, a high waist-to-hip ratio, and a large neck circumference--indicating a pre-diabetic state. That is not odd: A 2023 study showed that 136 million Indians are pre-diabetic, as we reported in August that year.

The patient also had pronounced dark circles under her eyes. Laboratory investigations revealed subclinical hypothyroidism and elevated evening cortisol levels, which disrupt the body's natural stress response and sleep cycle.

Kotwal attributed her condition primarily to light pollution or photo pollution--chronic exposure to artificial light at night during biologically-intended sleep hours.

Streetlights, illuminated billboards, neon signage, industrial and office lighting during night shifts, household lighting, and external security lights are the common sources of light pollution.

Kotwal’s prescription started with a series of light hygiene measures: installing blackout curtains, wearing an eye mask during sleep, and using blue-light blocking glasses after sunset. Blue light is emitted by electronic gadgets such as smartphones and tablets. She was also advised to avoid screens for at least two hours prior to her intended sleep time.

To restore the patient's circadian (24-hourly) rhythm through chronotherapy, Kotwal recommended scheduled bright light exposure in the early evening to increase alertness during her desired wake phase, followed by a gradual dimming of ambient light to cue sleep readiness.

Stress management practices, including mindfulness and deep-breathing exercises, were also advised. Regular monitoring and control of the thyroid-stimulating hormone and of blood glucose levels formed an essential component of her long-term care.

Diligent adherence to this integrative regimen helped the patient experience significant recovery. However, Kotwal noted that in certain individuals, especially those with persistent sleep disruption and heightened stress, melatonin supplementation or sleeping pills may be required. Left unaddressed, such circadian misalignment may put individuals at the risk of--or exacerbate--metabolic disorders like type-2 diabetes.

Anoop Misra, chairman, Fortis-C-DOC Centre of Excellence for Diabetes, Metabolic Diseases and Endocrinology, says clinical practice is increasingly showing up patients of hormonal imbalances and metabolic dysfunction such as diabetes, where light pollution and the ensuing stress and sleep disturbances are suspected contributors.

This is, perhaps, an outcome of 80% of the world living under light-polluted skies, according to a world atlas of artificial sky luminance generated in 2016.

Misra stressed the need to establish a direct cause-and-effect relationship between light pollution and metabolic disorders through controlled studies, which India has few of. However, a review of health studies conducted overseas shows that light pollution has a severe detrimental impact on human health, causing mental health issues, cancer and Alzheimer’s.

How artificial light at night causes disease

Being exposed to artificial light at night reduces the production of melatonin, popularly called “the hormone of darkness” since it is produced at night. Insufficient melatonin, in turn, disrupts the body’s circadian rhythm, the biological clock regulating the sleep-wake cycle. The fallout of this isn’t just the obvious sleep disturbances--exacerbated metabolic, hormonal and immunological imbalances are some of the other outcomes.

A study published in Sleep and Vigilance in January 2021 described the role of melatonin in the development and growth of cancer, immune activity, anti-oxidation and free radical scavenging (neutralising free radicals that can potentially harm healthy cells and tissues). Co-author Manisha Naithani, professor of biochemistry at the All India Institute of Medical Sciences, Rishikesh, explained that the damage starts in the part of the brain called the suprachiasmatic nucleus, when it receives light signals from photosensitive cells in the retina. The suprachiasmatic nucleus is a part of the brain, located in the front part of the hypothalamus, the central control of the endocrinological system. It works as the brain’s central clock, regulating the daily rhythm of the body.

Naithani’s study cites epidemiological evidence supporting the cancer link. “A Spanish study showed greater breast cancer risk and prostate cancer risk in people exposed to higher artificial light levels at night,” she said. “An Israeli study found a 73% increase in breast cancer incidence in areas with high night-time light.”

“Female shift workers such as nurses and police personnel have a higher breast cancer risk (see here and here),” she said.

Naithani pointed out that insufficient sleep is associated with hormone-sensitive cancers, meaning cancers that develop as an outcome of hormonal disturbances, such as breast, colorectal and endometrial cancers.

Some other side effects of exposure to artificial light at night are weight gain, gut inflammation, mood disorders and low resistance to environmental and emotional stressors.

A review study published in August 2024 established a clear link between light pollution and sleep disturbances leading to mood alterations, a finding in line with psychiatrists’ clinical experience.

“Poor sleep or insomnia is closely tied to depression and anxiety," said Kersi Chavda, consultant psychiatrist, P.D. Hinduja Hospital & Medical Research Centre, Mumbai. “People living in brightly lit urban areas often report feeling more stressed, anxious, or down. Night-time light exposure also makes seasonal depression worse for some, since the natural contrast between night and day gets blurred. Some victims find it harder to concentrate and think clearly during the day.”

Both Naithani and Chavda cited the blue light from a cell phone, and LEDs, as a key contributor to light pollution. “Blue-enriched light affects the suprachiasmatic nucleus the most, causing chronic stress and potentially triggering inflammation and lowering immunity,” said Naithani.

“Children, shift workers and those already dealing with mental health challenges are most vulnerable,” added Chavda.

Higher outdoor night-time light has also been linked with a higher prevalence of Alzheimer’s disease. In fact, it was found to be a bigger risk factor for Alzheimer’s than factors such as alcohol abuse, chronic kidney disease, depression, heart failure and obesity, according to a study published in Frontiers of Neuroscience last year.

The challenge, Naithani said, is that the “potential detrimental effects of artificial light are not known to all, the hidden perils of light are yet to be brought in full public knowledge so that night-time light can be dealt with effectively.”

Low awareness among those most exposed to light pollution

An online survey published in the Journal of Urban Management in September 2022 found very low awareness of light pollution among Indians aged 16 to 65 years--the age group that is most likely to have a nightlife and be exposed to various kinds of light pollution that the study described, such as light trespass, skyglow, over-illumination, light clutter and glare (see box).

Source: Journal of Urban Management

When respondents were asked how often they had heard of light pollution, 57% replied they hadn’t heard of it at all. When they were asked to explain light pollution, some of them said it referred to “violation of UV and other harmful rays in the sunlight”, “pollution which is not very harmful” and “maybe something related to environment”.

Consequently, the authors concluded that the lack of awareness extended the threat associated with light pollution.

Public lighting is widely perceived to contribute to safety but research does not prove this link. In fact, a study conducted in the UK showed that darkness does not increase the risk of certain types of crime. “Outdoor lighting may lower safety by making victims and potential theft articles more easily visible,” said Tanya Bedi, assistant professor, Department of Architecture, School of Planning and Architecture, Bhopal.

Poor enforcement allows light pollution to grow

Artificial light at night has been shown to increase with the growth of a country’s gross domestic product (GDP). But this association is deeper. It’s not the GDP volume as such that increases night-time brightness but the physical expansion of cities through real estate, highways, and urban sprawl, explained Bedi.

Essentially, “as a nation develops, infrastructure indicators such as road and streetlight density contribute to brightness levels,” she said.

Studies in India comparing light pollution over time show how much more bright the night sky has become.

Comparison of Light pollution in India between 2013 and 2023 (VIIRS-2013 & 2023)

Source: July 2024 study by Hasibur Rahaman Molla, Journal of Global Resources

A study by Bedi and others at the School of Planning and Architecture, Bhopal, identified Bengaluru, Kolkata, Hyderabad, Delhi and Mumbai as India’s most polluted cities from the perspective of light. Their research also found streets with illumination four times the Indian Standards recommendation.

A key reason for the excessive increase in night-time luminosity is the outburst of development with no strict regulations.

“Urban local bodies like municipal corporations, development authorities, and gram panchayats are responsible for public lighting,” said Bedi. “But compliance with the Indian Standards and the focus on curbing light pollution is usually hindered by a lack of awareness and specific regulations.”

Bedi’s study found the rampant use of low-mounted and densely packed luminaires, non-cut-off fixtures (fixtures that cannot direct the light downwards rather than upwards), and lamps of more wattage than required. Both administrative and local level measures are needed to reduce light pollution, she says.

Mumbai resident Nilesh Desai complained to the collector of Mumbai City about flood lights installed in the Wilson Gymkhana and the Police Gymkhana in Mumbai in 2017. Desai, who lives in the area, was disturbed by the excess lighting at night. The collector took prompt action, ordering the lights to be switched off at 10 p.m., and set up in a way that no resident is disturbed. He also instructed all gymkhanas to get prior permission to install lights.

Since then, Desai has also complained to the Brihanmumbai Municipal Corporation about lighting on construction sites that work round the clock, and digital hoardings, both of which are meant to be switched off at 11 p.m.

The challenge is: “after the pandemic no enforcement is happening,” said Desai. “Night matches in the Police Gymkhana start at 11 p.m., it is a pity that awareness about light pollution is very low. I have written to the police commissioner to switch off the Police Gymkhana lights after 10 p.m. but no action has been taken so far.”

Around the time Desai complained about light pollution from the gymkhanas near Marine Lines, Sumaira Abdulali, founder of Awaaz Foundation, a not-for-profit working on environmental issues, also studied light pollution in Mumbai.

“We found that coloured LED lights put up at Juhu beach for a ‘beautification’ project was contributing to light pollution,” Abdulali told IndiaSpend. “When we inquired, we were told that they were for safety but the light was focused and coloured so it could never serve to increase safety.”

“A review of street lighting on Mumbai’s main roads showed that it is quite effective in lighting up roads and isn’t intrusive,” added Abdulali. “However, what is intrusive and is getting worse over the years is lighting during festivals, and in recent years, digital hoardings, some building façades and construction sites, and advertisements of new properties. All these lights are intrusive, especially for drivers, in areas of natural beauty such as sea-fronts, and in residential areas, unless you use black-out curtains. Most people don’t use these, and why should they?”

Abdulali wrote to the BMC and objected to the BMC’s proposed hoarding policy, opposing brightly lit and moving digital hoardings as a safety hazard for drivers and a health hazard in residential areas. She was even called for a hearing in late 2024, but nothing has come of it as yet, she said.

IndiaSpend has reached out to the offices of the commissioners of the Brihanmumbai Municipal Corporation, the Municipal Corporation of Delhi and the Municipal Corporation of Greater Bengaluru. We will update this story when we receive a response.

What must be done to protect India from light pollution

A salient characteristic of light pollution is that it is localised and hence controllable. Unlike air pollution, it doesn’t spread on a windy day.

“Government authorities should promote better lighting design,” said Bedi. “State governments should adopt reference standards to control existing and proposed external lighting usage so that the concerned authority--municipal corporations in urban areas and gram panchayats in rural areas--can take necessary action towards responsible parties to resolve light nuisances and enforce dimming schedules for non-essential lighting during off-peak hours. Also practical issues like how tender specifications are framed, and limited technical capacity for monitoring lighting design must be addressed.”

Practical strategies to mitigate light pollution include mandating the use of full cut-off luminaires and environment-friendly backlight-uplight-glare (BUG) rated lighting fixtures to minimise glare and skyglow, said Bedi. “Further, energy efficiency concerns have pushed the widespread adoption of LEDs, but warm-toned LEDs can help reduce circadian rhythm disruptions in both humans and wildlife.”

Zoning can also play a key role in reducing light pollution. Creating lighting environmental zones, particularly in ecologically sensitive or biodiversity-rich areas, would allow for more adaptive and localised control, said Bedi. “Ward-level prioritisation maps would support a phased implementation approach, targeting the most ecologically vulnerable or light-polluted areas first.”

A lot can be done. But the experience of those who have complained shows that so far, light pollution isn’t being taken seriously enough.

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