EXHIBITIONS II: To the light fantastic

Across an infinite expanse of blackness, flickering red and green numbers sweep and swoop. Some move frenetically, others are almost still. They cross paths, but never collide: at just the moment when they might, they swerve. And as they plot their trajectories in random, cosmic choreography, they change: the red ones count up, from one to nine, and the green ones count down. Time moves as well as passes.

The creator of this galaxy is the Japanese artist Tatsuo Miyajima and its stars are LEDs (light-emitting diodes). He designed Running Time - in a collaboration with Artangel, the people who brought us Rachel Whiteread's House and William Forsythe's bouncy castle - especially for the Queen's House, Greenwich in 1995. Seen from the balcony above the Great Hall, it looked as if the contents of a digital clock had been shaken into a night sky and the numbers left to find their own way home. What the dazzled eye couldn't see were the 40 bumper-cars driving the LED numbers around the marble floor. Spaghetti junction met the solar system in a meditation on time and timelessness that was at once immense and intimate.

The spectacle will be recreated this week in Miyajima's first major show in Britain. "Big Time" comes to the Hayward from the Modern Art Museum of Forth Worth in Texas (the source of the gallery's last big hit, the Hodgkin retrospective). During the next two months, the lower spaces will be lit only by hundreds of LEDs flashing like fireflies. The exhibition is being installed by the architect Claudio Silvestrin - Running Time requires the construction of a see-through viewing bridge - and Miyajima is in town to see his counters, circuit boards and "U-cars" unpacked.

Meeting him, you feel that these bits of electronic wizardry are the stars of the show: the artist, despite his considerable height, cuts a low profile. And though he talks animatedly about his work, he wants it to speak for itself. His English is good enough for him no longer to need an interpreter, but it cannot match the eloquence or complexity of his art. The beauty of numbers, of course, is that they transcend language.

Born in Tokyo in 1957, Miyajima grew up wanting to be a carpenter, like his father. Instead he went to the Tokyo National University of Fine Arts and Music and became a performance artist. He has always been preoccupied by time - he has studied Buddhism, which he calls "a religion of time", for years - but in 1987 he narrowed his concerns down to three themes: "Keep changing, continue forever, connect with everything". Since then, he has concentrated on making installations that ask : do we exist in time, or it in us?

The works at the Hayward are his answers to that unanswerable question. All use LED numbers, but the time they mark is not real time: they count in numerical sequence, omitting zero, because it means death, but their movement is arbitrary; each number is an individual, but part of a harmonious whole; time is set in motion by the artist, but beyond his control. "It's completely about randomness," he says. "It's just a chaos, a chaos harmony." In Double Spiral, time appears as a snake without end. Big Number is a clock that ticks just once a week. The piece Miyajima is most excited about is Time in Blue, a changing series of newly invented blue LEDs. Like Yves Klein, Miyajima is fascinated by blue, not least because it's the colour of the sky, and "The sky is the first clock".

"Time is a very great mystery," he says, and when it inspires him to make visions as mesmerising as these, you hope it's a mystery he won't crack.

! Hayward, SE1 (0171 928 3144), Thurs to 17 Aug.