The weather man

Given the British taste for lying on windswept shingle in the name of pleasure, the success of Tate Modern's latest Turbine Hall installation should come as no surprise. The scale of its triumph, however, is another matter: since mid-October, when The Weather Project opened, some 600,000 people have poured in to inspect Olafur Eliasson's mock "sun", breaking visitor records since the converted power station opened as a gallery three years ago.

Spectators get up to all manner of things not normally encouraged in museums: they sprawl on the cold concrete floor in the semi-gloom, eating sandwiches, waggling their feet in the air. There's much serious kissing. Some are there to escape the real weather. Many are in a state of near trance. I swear I heard an "Ooohm" as I walked down the Turbine's ramp and along its 150m length. Only saffron robes and guru were missing.

For anyone whose head has been stuck in sand this past month, a reminder of the facts: The Weather Project by the 36-year-old Danish-Icelandic artist is the fourth commission (following Louise Bourgeois, Juan Muñoz and Anish Kapoor) to fill the gaping nave of the Turbine Hall. The installation consists chiefly of a large, yellow, mirrored arc of light which does not move. A fine mist, created by humidifiers pumping out sugar and water, creates an odourless faux " peasouper" - the kind of filthy coalsmoke smog of the 1950s which, ironically, the oil-powered Bankside Power Station was built to counteract.

In addition, the entire 35m high roof has been covered in mirrors so that you can look up at your ant-like ref lection, wriggle and wonder. Despite ardent and poetic claims to the contrary, this "sun" bears about as much resemblance to the real thing as do those fashionable wavy paper flames to a furnace. For the rest of us, it is what it is: a brilliant but intentionally imperfect optical illusion using 144 low-sodium light bulbs and 3,000sq m of glass. The puzzle is in trying to identify the nature of one's response: is it the size, the illusion, the dashed expectation of heat, the excuse to watch other people, neutralised into sallow anonymity by the mono-frequency light?

Eliasson, who, with the exception of a show in Dundee, has not exhibited in Britain before, is himself bemused. Tousled, serious, mildly disgruntled, having stepped off a plane straight into a scrum of press engagements, he shows a robust scepticism: "I haven't yet come to understand it. It is strange people say they can believe it really is the sun. It's quite clearly a construct. You can see how it's made. That's the idea. It's not an illusion but a metaphor, a filter for thinking about things, who we are, society."

Partly because of his quaint English, partly his unsettled state of mind, his often-abstract thoughts are not always easy to follow. He begins a quiet rant about the Saatchi-isation of art but, on being questioned, quickly retracts, saying he doesn't want to knock institutions or people.

"I don't know if I should even express my opinion but, to put it mildly, I think art has a social, ethical, moral content for society. This is because art is conceived fundamentally, not for a commercial idea. I know it's not that simple. But with Saatchi there's a kind of corporate branding in which work is taken out of context. So a great piece by Damien Hirst seems to lose its force. It makes art like items for sale in Oxford Street. But I must be careful not to moralise. I am not an institutional policeman. The potential of art is what interests me."

Born in Copenhagen of Icelandic parents - who had what he calls "normal jobs" - and now based in Berlin, Eliasson has a fascination for the point at which nature and urban life clash. In Los Angeles and Tokyo he poured non-toxic dye into rivers, turning them green; in S"o Paolo he froze a giant block of ice on the floor of a museum, though the exhibit had to close after enthusiastic visitors' slipping and sliding became too dangerous. All his work, including The Weather Project, he says, has won a following without the aid of celebrity or fashion.

"It hasn't got big because someone famous was seen here. In London, impressively, and unlike any other city, art has filtered through to the public imagination. Most people could name a contemporary artist or two. People aren't afraid to come to Tate Modern. And it's free. It's not that there's anything wrong with lifestylemagazine art shows. It's not that an Armani or Andrew Lloyd Webber show is worse. It's just that my Tate piece is rather plain, flat, slightly profane and I like that." But is it chiefly about people, or the sun, or something we call art? "It's definitely first and foremost about people. People are looking at themselves as much as at art. If that's a good thing, I don't know. It's all part of the discussion."

Eliasson follows a wellestablished tradition of making art out of weather. Think of the solar deities of the Druids or Pharaohs, Turner's sunsets, Constable's cloud studies, Cotman's rainbows, Van Gogh's burning skies. Despite a conventional art-college training in which he drew, painted, studied these masters of the past, Eliasson does not appear to hold much store by them. Being married to an art historian, he has every chance to find out. He is more interested, however, in the Gestalt therapy and neurology he studied during his time at the Royal Academy of Arts in Copenhagen in the early 1990s.

"I come to this more interested in the psychological impact of weather than the visual effect. It's something we share. Although the British like to boast they talk about it more than anyone else, that's just not true. We do in Denmark. Canadians are obsessed. Weather is crucial to the farming and fishing industry. It's about survival and whether you have a house next year. That generates a sense of community. And I like to do things with machines. I have people to help me work things out." To this end he employs an architect, a carpenter, a blacksmith, an engineer, a mathematician-geometrician and a structural designer.

After the Weather Project, which runs until March, Eliasson has a show in Iceland. He is busy. He is successful. He checks watch and mobile frequently. A TV interview beckons. As a parting shot I ask his view of the soaring hotel atrium in which we have met - a mini Kew Gardens or Eden Project with 30ft palms, elaborate displays of unseasonally blooming lilies and irises and a fantasy array of surreally gleaming succulents. "Huh?" he grunts. "It's like a hotel lobby." Olafur Eliasson is not one to fall for illusion. So if you venture to Turbine Hall for a bit of sun worship, remember it's all done with mirrors. However deep the experience you are having, it won't even harm your skin.