Reported by BBC World
Millions across India are celebrating Diwali, the Hindu festival of lights, illuminating homes, temples, offices and streets with oil lamps and colourful lights to symbolise the triumph of light over darkness.
The festival falls on the darkest night of the Hindu lunar month of Kartik, when the moon is not visible in the sky.
Although Diwali traditions vary across India's regions and communities, the festival is widely marked by prayers, family gatherings, the exchange of sweets and the lighting of firecrackers.
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But the celebrations come amid growing concerns over air pollution , particularly in northern India.
Seasonal weather conditions and the burning of crop residue contribute to deteriorating air quality, while firecrackers set off during Diwali can make the situation worse.
Air pollution in the Indian capital Delhi has reached such hazardous levels that it is the most polluted Diwali festival in a decade. New measures to improve air quality do not seem to have been successful.
India's financial capital, Mumbai, has also experienced high pollution levels in recent weeks.
In an effort to limit pollution, India's Supreme Court on Monday permitted the manufacture, sale and use of certified "green" firecrackers in Delhi and surrounding areas for a limited period.
These firecrackers are designed to produce 20-30% fewer emissions than conventional fireworks. But critics have questioned how effective they are at reducing pollution and raised concerns that conventional firecrackers could still make their way into the capital from neighbouring states.
Repeated violations of firecracker restrictions leave cities grappling with worsening post-Diwali smog
Despite the debate over fireworks, Diwali is about much more than firecrackers.
The festival celebrates the return of Lord Ram to Ayodhya after his victory over Ravan, the main antagonist in the Hindu epic Ramayana, and symbolises the triumph of good over evil, light over darkness, and knowledge over ignorance.
In the days leading up to the festival, families clean and decorate their homes with flowers, colourful lights and traditional oil lamps known as diyas.
The celebrations also bring families and friends together for prayers, elaborate feasts and the exchange of gifts, and lots of traditional Indian sweets.