Millions across India are set to celebrate 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.

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.

In the capital, Delhi, the air quality index (AQI) reached 391 on Friday morning, placing it in the "very poor" category ahead of the festival.…