The sky is a dull grey, and I expect it to stay that way. I will turn out to be wrong. Not because the weather is going to change – the clouds will continue to drag themselves, blank and featureless, over the port city of Aarhus, Denmark, for the entirety of this January day. But because I am about to meet James Turrell, an artist who works in the medium of light, who has promised to show me a new artwork that could turn this grey sky blue – or any other colour that I could imagine.

We meet inside the ARoS art museum: Turrell, 83, arrives in a wheelchair pushed by his wife Kyung-Lim Lee, a Korean-born artist. Dressed in a fine navy three-piece suit and gleaming oxblood cowboy boots, he looks the very model of an upstanding gentleman of the old west, fresh from his ranch outside Flagstaff, Arizona.

He stands – he can walk, but not with great ease – and takes a seat. Museum staff serve him black coffee and a glass of iced water. They treat him with the hushed reverence befitting one of the greatest living American artists, whose installations scramble the senses and sell in the high six figures. “I always wanted people to value light,” he begins. “In art, people – particularly collectors – are always looking for treasure. That’s why painting still holds force, though we’ve gone forward in the world. And I paint with light. I use light to work the medium of perception.”