the day Anthony McCall realized that his light sculptures were alive

In early 1973, Anthony McCall, sculptor of light, was 26 years old and had made a splash with his first piece, Landscape for Fire. This was a film of a performance in which ghosts dressed in white ignite fires across a vast landscape, experimenting with McCall's belief that a performance is not a performance unless it is documented in some way. "If it takes place in the middle of nowhere," he says, "you have to record it."

Half a century later, I meet him at Tate Modern in London, which is about to launch a major exhibition of his immersive, ...