If you have doubts about art made from light, consider Michelangelo's Pietà. Deeply incised, highly polished, the work breaks itself down into shadow and gloss, the chiaroscuro of the Resurrection told as a tale of dark and light. Were you to lock the Pietà in a blackened room, it would, conceptually, cease to exist. Having seen Light Show at the Hayward Gallery, I'm surprised no one has thought of it.
After all, the kind made by sound artists apart, art has always been light art. The work in Light Show is different from Michelangelo's only in that it is active rather than passive, generating its own luminosity rather than stealing it from elsewhere.
The light here is electric, which is to say artificial, which is to say new. Underlying all the work in Light Show is a Promethean anxiety, a wonder at (and lurking fear of) modern man's ability to make light for himself. Light is what we see by: no light, no vision. If that light is artificial, then so, potentially, is what it allows us to see. Something at the heart of the way we believe – an idea of enlightenment, of revelation through light – is made uncertain. We are like the captives in Plato's cave, only worse, seeing what we see more brightly than they do, but with all the less assurance that it is real.
Phew. If that sounds as though Light Show is going to make for heavy viewing, then the opposite is true. The art in it tends towards the twinkly. Thus the first work you see as you walk in, Leo Villareal's Cylinder II – a 20-foot column of white LEDs, bubbling effervescently like a 7-Up ad. Villareal's work could be at Piccadilly Circus, except that all it advertises is itself. That, I guess, is the point. Cylinder II seems to be telling us something, selling us something. But in the end it is merely pretty, a closed loop, a self-answering question.
There is a lot of that in Light Show, fiat lux without the accompanying enlightenment. Across the way from Villareal's column are half a dozen more by Cerith Wyn Evans, in S=U=P=E=R=S=T=R=U=C=T=U=R=E. As often with Wyn Evans, these pulse out a message like so many chandeliered Aldis lamps. But where his older works did this in an actual language – the dot-dot-dash of Morse code – S=U=P=E=R =S=T=R=U=C=T=U=R=E broadcasts incoherently, as light-music rather than light-language. Could you decode Wyn Evans's pulsings, you would, apparently, find yourself reading the transcript of a Ouija séance: but you can't. Light is not an agent of revelation, but of ever greater mystification.
Wyn Evans says that the idea came to him as he was looking down at the lights of Tokyo, and that, at least, is revealing. The invention of plate glass in the 1830s led to the vast shop windows of the grands magasins of Paris – before, they would have been divided into small panes. This, in turn, allowed Parisians to window-shop in a single gaze, a new kind of buying and a new kind of seeing tied to each other. Next stop, Manet. In the same way, electric light has changed the way we see, and specifically the way we see urbanly.
If a single thing unites all the work in Light Show, it is its response to urbanity. For David Batchelor's Magic Hour, the bright lights of downtown are endlessly romantic. In this work, Batchelor's trademark light boxes turn to face the wall. The diffuse glow they emit has the feel of a sunset obscured by buildings; the cracks of light between the boxes etch a grid like a city block seen from the air. Magic Hour is a distillation of urban beauty, urban seeing.
At first glance, James Turrell's Wedgework V could not be less like Batchelor. Actually, they are rather alike. For any Turrell, part of the experience is pilgrimage – through the Arizona desert to his unfinished Roden Crater, down a perilously dark corridor to Wedgework V.
At the end of this is a darkened room, its miasmic far wall set at an angle. You sit on a bench and wait: a sign warns that it may take 15 minutes to see Turrell's meaning. The wall glows red, and red again; and then, slowly and then suddenly, it begins to … I'm not sure of the word. Change colour, yes, but also change dimension, energy. It is like a Rothko come to life, beautiful and horrifying at once.
You want to run away and to stay for ever. I hesitate to use the word "religious" to describe any artwork. Were I to break that rule, though, it would be for Wedgework V. Perhaps one day Turrell, a Quaker, will be allowed to make his own answer to Rothko's Houston chapel: I would certainly travel to see it. In the meantime, make sure you see Light Show. It is marvellous.
To 28 April (020-7960 4200)
Charles Darwent attends the birth of Picasso at the Courtauld Gallery
Master of the collage, Kurt Schwitters gets a substantial show at Tate Britain, until 12 May. German by birth, the artist died in the Lake District having spent eight years there working in relative obscurity after fleeing the Nazis – and it's these final years that are illuminated in this show called Schwitters in Britain.