The blockbuster retrospective by the world-famous American artist is less than two months into a six-month season at the National Gallery, with tickets disappearing fast.

But not as fast as everyone thinks, the gallery is keen to point out, with plenty of tickets still available for the show, both pre-booked and on the door, and sessions every 15 minutes.

However many visitors, especially those from interstate, will miss out of the show's much-vaunted centrepiece – an experience inside the Perceptual Cell, the white metal sphere that allows just one person at a time for an intense 15-minute light display.

Premium tickets that include the cell experience have already sold out on all weekends until the end of the exhibition in June, as well as all of March and much of April, especially on Fridays.

The show, made up mainly of several large-scale light installations, is set out in such a way that only 120 people can be inside the displays at any given time.

While this is good news for gallery-goers wanting the full benefit of Turrell's immersive light experiences, it has made for an unusually intricate booking system.

Visitors can choose, via Ticketek, from three options – a weekday visit, a weekend visit with longer hours, or a premium experience that includes 15 minutes inside the Perceptual Cell.

This last option is apparently the one causing the most angst, as individual visitors must book an exact time slot in advance.

Many booking online have also been hit inadvertently with double booking fee – $5 per ticket – when booking for more than one person, believing they can only buy one ticket at a time for the Perceptual Cell.

In fact, it is possible to save one slot and return to the booking page to select another and only be charged a booking fee once, although a spokeswoman from the gallery admitted that the system "might not be intuitive" for many gallery-goers.

She advised reading the small-print messages that popped up at various junctures throughout the booking process that explain the fees involved.

Assistant director in charge of exhibitions Adam Worrall said the show had been every bit as popular as the gallery had hoped, and the word seemed to be spreading.

The show is one of a series of retrospectives of the artist's work, including a 2014 season at Guggenheim Museum in New York, which recorded its highest attendance rate ever during the show's run.

Interestingly, Mr Worrall said, for one of the first times in the history of the gallery's blockbusters, Canberrans had been among the earliest and most voracious visitors to the show, instead of waiting until the final weeks to front up and see what the fuss is about.

"We have been thrilled to see really strong visitor numbers from Canberra and I think that is because of [Turrell's work] Sky Space outside in the garden – people here really understand the power of James Turrell's work and got in quick over the holiday period," he said.

But he said the popular notion that the entire show was sold out completely was incorrect, and while it was advisable to book ahead, many visitors had been pleasantly surprised to be able to buy tickets at the front counter on arrival.

James Turrell: A Retrospective is at the National Gallery of Australia until June 8.