The Duchess, who is on her third official visit to the country, has become something of a dab hand at dressing elegantly for the heat. On Wednesday she looked cool and fresh in a salwar kameez-style oufit, consisting of a pale blue tunic top and flowing white trousers.
The ceremony took place on the banks of the River Ganges in the holy city of Rishikesh. Located in the foothills of the Himalayas, the city rose to international fame when the Beatles visited in 1968.
During the ritual, residents of the nearby ashram of Parmarth Niketan, lit lamps and sang devotional songs, led by young boys dressed in yellow robes.
Held to thank God for the light he has provided during the day, it takes place every evening come rain or shine. Until recently it was held beneath a 14ft-high statue of the god Shiva but that was destroyed by flooding a few months ago.
Prince Charles is fascinated by Indian culture and last year spoke of his "particular affection" for that part of the world. He described growing up listening to stories about the Sub-continent, presumably from his great uncle Lord Mountbatten who was the country's last viceroy.
November's trip includes a visit to one of the world's largest Hindu temples, which is in New Delhi, and to one of the oldest synagogues in the Commonwealth at Kochi.
In Mumbai, the royals plan to pay their respects to victims of the 2008 attacks, meeting with staff from the Taj Mahal hotel who saved the lives of guests by guiding them to safety during the atrocity.
The couple will also mark Remembrance Sunday in India and the future King's 65th birthday on November 14.
Charles and Camilla will spend one day in private the day before his landmark celebration enjoying the breaktaking scenery in Kerala to the south west of the country.