Evening in a large garden in Chandanagore, a small town on the banks of the river Hoogly, 40km north of Calcutta. The mayor is there, so is the British high commissioner and his bodyguards, a few neighbours and the plain curious. The occasion is the switching-on of Sridhar Das's latest animated masterpiece, Bajra: a great ornamental peacock boat.  As the moon rises, a generator comes on, and with a furious clicking and whirring an ancient belt-driven fan motor starts up. Some 125,000 tiny handmade light bulbs, each wrapped in coloured sweet paper and carefully tied up with cotton, start to switch themselves on and off. The 7m-long, 5m-high boat begins to move, ploughing through pools of light. Its orange and gold wings flap lazily, a fantastical sun radiates yellows and blues and its turquoise and vermilion tail pulses.  The assembly applauds, but a 60-year-old man and a young woman sit quietly in the shadows. Das, the boat's maker, has been weaving two-dimensional tapestries of light like this for more than 50 years. "It's good", is all he says. Nandita Palchoudhuri, its Calcutta-based designer, is also pleased, but both worry about the boat's next voyage: in the hold of a freighter bound for the Thames festival, where it will spend two days on the South Bank before being processed in a carnival of light along the embankment.  Chandanagore is the capital of Indian illuminations. The small town employs up to 12,000 people, who work nine months of the year creating extravagant shows for major festivals. Das is the town's most renowned light artist. In the past few years, he has made waterfalls, monkey gods, dragons spewing fire, the triumph of good over evil, portraits of Nobel prizewinners, political statements, environmental messages, even pontifications by politicians.  His workshops are a cross between a foundry and a tapestry studio. Four or five men may work together on a tableau, rapidly stitching the lights individually into the wire frame. Each may need 30,000 lights. The peacock boat, which took 10 people two months to make, uses miles of wire, and when switched on needs a staff of three electricians to watch over it and tend it like a garden.  In London, the boat will be processed along the embankment at the head of a mile-long "river of light", produced by thousands of performers in illuminated costumes walking along the Thames. Das will be there among the crowds, doing what he does in Calcutta at festival time each year. "I wrap myself in a shawl and listen to what people are saying about the lights. I'm not especially proud of them, except that I know that I make them better than anyone else."  · The Mayor's Thames festival takes place this weekend, with the parade of lights on Sunday evening. Details: Thamesfestival.org
Take 125,000 light bulbs, miles of wire and three electricians. Then flip the switch. John Vidal sees India's best illuminated art.