Light Pollution in India's Cities: A Satellite Data Analysis

Which Indian cities have the worst light pollution -- and where can you still see the Milky Way?

India adds roughly 10 million people to its urban population every year. New highways, commercial districts, and residential towers bring prosperity and opportunity. They also bring something less welcome: a sky that is disappearing.

For the 500 million Indians living in cities today, the Milky Way is already invisible. Most urban children have never seen it. And the problem is accelerating -- India's artificial light emissions are growing faster than almost any other country on Earth.

We decided to measure exactly how bad things are, city by city, using satellite data covering the entire country.

How We Measured India's Skies

SkyQI combines two complementary data sources to map light pollution across India:

VIIRS Satellite Data -- NASA's Visible Infrared Imaging Radiometer Suite orbits the Earth nightly, measuring artificial light emissions from space. We process 60,681 grid points covering India, converting raw radiance values (measured in nanowatts per square centimeter per steradian, or nW/cm2/sr) into sky quality estimates.

Ground-Level Smartphone Measurements -- Users upload night sky photos through SkyQI, which our algorithm analyzes for star counts, sky brightness, artificial light contamination, and color temperature. These ground-truth measurements validate and refine the satellite estimates.

The conversion pipeline works as follows: VIIRS radiance values are mapped to SQM (Sky Quality Meter) readings using an established logarithmic relationship. SQM values are then classified on the Bortle scale, a 1-to-9 system where 1 represents pristine dark sky and 9 represents an inner-city sky where only the Moon and planets are visible.

As a general reference: radiance below 0.5 nW/cm2/sr corresponds to Bortle 1-2 (dark sky), 1-5 nW corresponds to Bortle 3-4 (rural), 5-20 nW to Bortle 5-6 (suburban), and anything above 20 nW pushes into Bortle 7-9 (urban to inner-city).

India's 10 Brightest Cities

The following estimates are derived from VIIRS satellite radiance data for urban cores. Actual conditions vary by neighborhood -- even within a single city, sky quality can differ by 2-3 Bortle classes between a brightly lit commercial zone and a quiet residential area.

What the Numbers Mean

Mumbai leads the list, with some areas in South Mumbai and along the Western Express Highway registering radiance values above 300 nW/cm2/sr. At Bortle 8-9, only the Moon, planets, and a handful of the brightest stars are visible. The Milky Way is completely obliterated.

Delhi NCR is a close second. The combination of dense urban development, highway lighting, and the massive Connaught Place / Lutyens zone creates a dome of light visible from over 100 kilometers away. Even in relatively quiet areas like parts of South Delhi, the Bortle rating rarely drops below 7.

Bangalore has seen some of the fastest growth in light pollution, driven by the IT corridor expansion along the Outer Ring Road and Whitefield. A decade ago, dark skies were accessible within a 30-minute drive from the city center. Today, you need to drive over 80 kilometers.

Pune, Jaipur, and Lucknow offer a sliver of hope. While their urban cores are heavily light-polluted, their smaller footprints mean that reasonably dark skies (Bortle 4-5) can be reached within 40-60 kilometers. From the outskirts on a clear moonless night, a faint trace of the Milky Way may be visible -- but it is a shadow of what our grandparents saw.

The Indo-Gangetic Plain Problem

One pattern in the VIIRS data is particularly alarming: the Indo-Gangetic Plain, stretching from Punjab through Uttar Pradesh to Bihar, shows an almost continuous band of elevated radiance. Individual cities are merging into a single, unbroken corridor of light. Towns that were once dark buffers between cities -- places like Panipat, Karnal, Muzaffarnagar -- now register Bortle 5-6 readings.

This urban light corridor is visible from space as a bright arc across northern India, and it is expanding every year.

India's Darkest Corners: Where Stars Still Rule

The good news: India still contains some of the finest dark sky locations on the planet. The same VIIRS data that reveals urban light pollution also confirms pockets of extraordinary darkness.

Ladakh -- Hanle and Pangong (Bortle 1-2)

India's darkest skies are found in the high-altitude desert of eastern Ladakh. Hanle, home to the Indian Astronomical Observatory at 4,500 meters elevation, became India's first International Dark Sky Reserve in 2022. VIIRS radiance here drops below 0.2 nW/cm2/sr -- effectively zero artificial light. The Milky Way casts visible shadows, the zodiacal light is prominent, and the Andromeda Galaxy is visible to the naked eye.

Why it is dark: Extreme remoteness (the nearest significant town is hours away across high passes), low population density, high altitude placing observers above 40% of the atmosphere, and cold dry air that minimizes atmospheric scattering.

Spiti Valley, Himachal Pradesh (Bortle 1-2)

The rain shadow region beyond Rohtang Pass is one of the least light-polluted inhabited areas in the world. Villages like Kibber, Langza, and Komic sit above 4,000 meters with virtually no artificial light on the VIIRS map. Spiti combines the darkness of Ladakh with slightly easier accessibility (by Indian mountain standards, at least).

Rann of Kutch, Gujarat (Bortle 2-3)

The vast salt flats of the Rann offer something unique: an unobstructed horizon in every direction. With terrain as flat as the ocean and minimal settlements, the Rann provides panoramic sky views that few locations can match. During the Rann Utsav festival season, light pollution increases near the tent city, but the deeper Rann remains pristine.

Western Ghats -- Coorg, Valparai, Kodaikanal (Bortle 3-4)

For stargazers in southern India who cannot trek to the Himalayas, the Western Ghats offer the most accessible dark skies. Coffee plantations in Coorg, tea estates near Valparai, and the hills around Kodaikanal all provide Bortle 3-4 conditions. These are not pristine -- you will notice light domes on the horizon from distant cities -- but the Milky Way is clearly visible and hundreds of stars fill the sky.

Andaman and Nicobar Islands (Bortle 2-3)

Oceanic darkness is a special thing. With no landmass for hundreds of kilometers in most directions, the Andaman Islands experience sky conditions that are among the darkest in India. The VIIRS data shows near-zero radiance outside Port Blair. For anyone already planning a beach holiday, the night sky is a remarkable bonus.

The Cost of Losing the Night

Light pollution is not just an aesthetic problem. India wastes an estimated $800 million annually on misdirected outdoor lighting -- light that shines upward into the sky instead of downward where it is needed. That wasted energy translates to roughly 1.23 million tonnes of CO2 emissions per year, equivalent to putting 500,000 additional cars on the road.

The health consequences are equally serious. Artificial light at night disrupts circadian rhythms, suppressing melatonin production and increasing risks of sleep disorders, obesity, and certain cancers. A 2022 study published in eBioMedicine found that outdoor light exposure at night was associated with a 13% increased risk of breast cancer and a 25% increased risk of lung cancer.

Wildlife suffers too. India is home to thousands of migratory bird species that navigate by starlight. Bright urban corridors disorient birds mid-flight, leading to fatal collisions and exhaustion. Sea turtle hatchlings on India's coastlines crawl toward city lights instead of the ocean. Insect populations -- the foundation of countless food chains -- are decimated by the fatal attraction of artificial lights.

What You Can Do

1. Measure Your Sky

The first step to fixing a problem is measuring it. Upload a night sky photo to SkyQI and get an instant Bortle rating for your location. It takes 30 seconds, and your measurement joins a growing database of ground-truth observations across India.

2. Compare and Share

Look up your city in the SkyQI map. Compare your neighborhood to others. Share your results -- when someone in Delhi sees their sky rated Bortle 9 while a village in Ladakh rates Bortle 1, the contrast is visceral and shareable.

3. Advocate for Better Lighting

Light pollution is one of the most solvable environmental problems. It does not require new technology or massive investment. It requires:

• Shielded fixtures that direct light downward, not into the sky
• Warm color temperatures (under 3000K) that reduce atmospheric scattering
• Motion sensors and timers to eliminate all-night illumination of empty spaces
• Dimming during late-night hours when full brightness is unnecessary

Many Indian cities are currently installing millions of new LED streetlights under the SLNP program. The choice of fixture design and color temperature being made right now will determine India's night sky for the next 20 years.

4. Support Dark Sky Initiatives

India's dark sky movement is growing. Hanle's International Dark Sky Reserve status in 2022 and Pench Tiger Reserve's Dark Sky Park certification in 2024 demonstrate that conservation-minded designations are achievable. Advocate for dark sky protections near astronomical sites, wildlife reserves, and national parks in your region.

The Clock Is Ticking

Every year that India delays addressing light pollution, the problem becomes harder to reverse. Light domes around cities expand. The Indo-Gangetic corridor brightens. Dark buffer zones between cities vanish.

But every measurement helps. Every data point on the SkyQI map makes the invisible visible. And every conversation about the night sky we are losing plants a seed.

Take a photo of your sky tonight. See what the satellites see. And decide whether the stars are worth saving.

Measure your sky at skyqi.in