The mesmerising world of Edward Hopper

A rare exhibition by one of America's most distinctive artists opens at Tate Modern later this week.Tom Lubbock analyses his appeal

Edward Hopper is famous and hardly known. The images of the American painter are widely loved and published, in posters, postcards, picture books. We think we know them, these poignant myths of modern solitude - the lonely rooms, late bars, anonymous lobbies, isolated gas stations, empty streets. But how many have seen a Hopper face to face? There is (I'd guess) not a single Hopper painting in a British collection. There hasn't been a Hopper exhibition here for 20 years. On Thursday Edward Hopper opens at Tate Modern, a full retrospective, showing through the summer. You may be surprised.

In reproduction,the pictures look good, and they look like they don't lose much either. Hopper's enigmatic theatre comes across so strongly. You get his elusive human stories, never spelled out, and his dreamlike settings that are strangely under-described, as if made from a few clearly remembered details, and always with something more, unseen, off-picture. You see his dramatic illumination, shafts of sunlight striking onto walls, electric-lit rooms glowing out of the night, and his bold colours and designs. And you can probably tell, if you look through a picture book, that Hopper's painting goes off. The figures become clumsier, the dramas less sharp.

But in front of the paintings, all these things are changed. The pictures have a direct visual-emotional impact that reproduction never hints at. Or rather, some of them do. And many others, often the ones that seem most atmospheric in reproduction, even the classics like Nighthawks and Office at Night, conspicuously fail as paintings.

So the surprise isn't quite what you'd expect. It doesn't go one way. It's not that Hoppers turn out to be generally better in actuality, nor that they're better as illustrations. No, the odd thing is, his work has a stark double life. There are pictures that are good as posters, but bad as paintings. And there are pictures you might flip past in a book, but on the wall they're utterly gripping, piercing.

Hopper found form late. A New Yorker, born in 1882, he spent a long time being a bit of an artist and a bit of a commercial illustrator and for about 10 years gave up painting almost entirely. In 1924 he began to paint again. Immediately the work arrives in full force. In the pictures from the 1920s and the early 1930s, Hopper's world is there complete - in Early Sunday Morning, say, a deserted stretch of street, in Drug Store, a lit shop window at night, and in other nocturnes like Automat, a woman alone in a café, or Night Windows, a woman fragmentarily glimpsed in an upstairs room. And these are the paintings that have the real presence.

The colours here are so startling, with quite unexpected harmonies and intensities. More than that, the colour schemes attune with the mood and space of the scenes. Take a picture like Sunday, a bald man sitting on a sidewalk in front of some closed shops. In Hopper books I've glanced at this image, barely pausing over its dull greys and browns, marking it down as a dud. But in its true colours, it's a spellbinder. The vacant wooden shop-fronts, the air in front of them, are alive with a mesmeric emptiness and blankness.

It's a spell that later pictures very rarely recapture. Hopper worked on for decades, dying in 1967. There's painting after painting in Tate Modern where a promising scene is set, but without that true grip of colour and space and feeling. It can suddenly reappear, as in the very late Intermission, a woman sitting alone in an emptied auditorium, with a great void of blue wall behind. It's striking how clear the difference is. But to describe this spell precisely, let alone account for it, is tricky. All the usual stuff about loneliness, sadness, alienation - it's not exactly wrong, but it feels off the point.

Some things about a good Hopper are plain. There must be no more than one figure, a single consciousness to focus the feeling of the space. It's rather as in Munch's The Scream, where you can't say whether the figure is screaming the sky, or the sky is screaming the figure. In Hopper's more muted images, scene and figure absorb one another. It must be only one figure, one mind absorbed. The pictures from the 1940s, like Nighthawks, resembling movie-stills, lose it. Several figures - and at once there's a drama, an interaction among people, a distraction from the central relationship between the figure and the place.

It's important this one figure has no strong expression. The face should be composed, or even hidden, looking away, lost in shadow. It's not about how people are feeling, sad or lonely or ill at ease or whatever. It's about a state of going deeply blank, about becoming a thing in a world of things. This is the real reason why the figure must be alone. There must be nobody else to see them as a fellow human. And this is why Hopper puts his solitary figures in public places, in a street or an auditorium or a café, in places where they might well be on view. It's to emphasise that they aren't. The young woman sits with her coffee in Automat, glaringly lit, and unseen. No one is looking at her.

No one: not even you, the viewer.

That's the weirdest effect. I don't how Hopper gets it. The things in the pictures look like things that aren't being looked at. The man or woman is completely, completely alone. As you look at them, you feel that your viewpoint is unoccupied, that you aren't there. It's a scene without a viewer.

This is why it's a mistake for Hopper to get too sexy. The later pictures often become rather obvious sex fantasies. He's painting a woman, sometimes naked, to excite himself. (It's always a version of his wife.) He gets interested in the breasts and the bottom, enlarging them, improbably reshaping the body to get the maximum of everything in view. So even when these female figures are meant to be solitary, clearly they're not. They are being thoroughly looked at. Hopper's spell, the scene without a viewer, is broken.

But when the spell holds, it holds just as strongly in deserted places, where there's no figure at all. The New York street shown in Early Sunday Morning is entirely unpeopled. There is no one in it, no one looking at it. The bright illuminated pharmacy window in Drug Store, with its sign saying "Prescriptions Drugs Ex-Lax", is blazing away on a street corner though the night, advertising itself - to nobody.

"When we were at school," Hopper once remembered, "we debated what a room looked like when there was no one to see it, nobody looking in, even." People often talk about that kind of thing. They don't often find a way to paint it, as Edward Hopper found, for a short stretch of his career, painting a transfixing blank, a world from which human perspective has been withdrawn. And the rest of it, the atmospheres, the enigmas, the melancholy; powerful as it is, the rest is posters.

Edward Hopper: Tate Modern, 27 May-5 September, open every day, admission £9, concs £7; late night opening 10pm, Fridays and Saturdays. For more information, go to www.tate.org.uk or call 020-7887 8888