A Gurugram schoolgirl built a free website that measures light pollution from phone photos; Suhani Gupta has analysed night skies across 50 Indian cities to show how artificial light is changing them

For most of the kids who grew up in a village or some place where night skies were clear and visible, spotting seven stars is normal. But for those in the cities, pollution makes it a difficult to impossible task sometimes. Growing up in a city where artificial lights often obscure the night sky, Suhani Gupta started wondering why stars were becoming increasingly invisible! She became more curious about the subject and that curiosity led her to develop SkyQI, a free online platform that measures night-sky brightness using ordinary smartphone photographs.As reported by The Better India, the Class 12 student has also analysed satellite data from 50 Indian cities, finding that median night-time radiance increased by 70% between 2015 and 2025.Suhani’s invention

Stars in the sky (Canva)

Suhani’s interest in the subject started in 2024. She was part of her school’s space society. During meteor showers and other astronomical events, students would gather online, sometimes around 3 am, to observe the night sky.She initially believed that air pollution and haze were responsible for the limited visibility. However, visits to her grandparents in Udhampur, Jammu and Kashmir, made her notice a difference.The skies there appeared much darker, and more stars were visible with naked eyes.The contrast made her realise that another form of pollution could be affecting what people saw above them which was ‘light pollution’.Unlike air or water pollution, light pollution is not always immediately recognised as an environmental problem. As cities expand and outdoor lighting becomes more widespread, the gradual disappearance of natural darkness can go largely unnoticed.Suhani then started exploring whether the problem could be measured without expensive scientific equipment.Turning a smartphone into a light pollution detectorIn May 2025, Suhani developed SkyQI, a website that could estimate the brightness of the night sky using photographs taken on ordinary smartphones.Professional astronomers generally use specialised instruments called Sky Quality Meters (SQMs) to measure night-sky brightness. However, these devices can be expensive and are not easily accessible to students. Suhani wanted to make the process simpler.Her parents

Clear sky (Canva)

Both her parents, both software engineers who studied at BITS Pilani and helped her understand the technical concepts. Her mother introduced her to image processing, while she learnt Python.The initial version of SkyQI assessed the overall brightness of a photograph. But she soon realised that this approach was not reliable enough as clouds could make the sky appear brighter.She subsequently redesigned the platform to examine three indicators: the number of visible stars, the difference in brightness between the horizon and the sky directly overhead, and the calculated brightness of the sky.The website went liveSuhani also introduced safeguards to account for variables such as cloud cover, camera settings and image quality. For photographs without complete camera information, the platform uses satellite-based light pollution data to help estimate the conditions.However, SkyQI has not yet been validated against a professional Sky Quality Meter, and its readings should be treated as estimates rather than replacements for specialised scientific instruments.According to figures shared in The Better India report, the platform had received 1,198 photographs from more than 490 contributors across 63 countries. India was its third-largest source of observations, after the United States and China.What did her study of 50 Indian cities reveal?

Suhani Gupta (Better India)

In 2026, she analysed a decade of NASA satellite observations covering 50 Indian cities, comparing night-time radiance in 2015, 2020 and 2025.Her findings, published in the India’s Darkest and Brightest Cities 2026 report on the SkyQI website, revealed that median night-time radiance across the 50 cities was 70% higher in 2025 than in 2015. As many as 47 cities recorded an increase.One of the most striking findings concerned Leh in Ladakh. Despite its reputation for relatively dark skies and astronomy tourism, the city recorded a 546% increase in satellite-observed night-time radiance over the decade.Other popular destinations known for their scenic night skies also showed increases. Shimla recorded a 165% rise, Jaisalmer 151%, Manali 136% and Rishikesh 118%.The report also identified Bengaluru as India’s brightest city in its 2025 dataset, followed by Delhi and Hyderabad.For her analysis, Suhani used NASA’s Black Marble dataset, which draws on observations from the Visible Infrared Imaging Radiometer Suite (VIIRS) aboard the Suomi-NPP satellite. NASA uses this satellite-based information to monitor artificial lighting and changes in human activity across the planet.