Let there be magical light

Seasonal affective disorder (SAD) hadn't even been discovered when Sir John Soane (1753-1837) experimented with light levels to pack an emotional charge within his own house at 13 Lincoln's Inn Fields. And it would be at least 100 years before the world's first light bulb was a twinkle in Thomas Edison's eye. Yet Soane understood all about the impact of light on space, using direct and indirect sources to change mood and alter perceptions of space. Luckily for us, he bequeathed his house to the nation in a special Act of Parliament. That house did not make Soane a household name in his lifetime, but an exhibition that's just opened at the Royal Academy of Arts will.

Architectural exhibitions are notoriously difficult to stage, full of plans and elevations to baffle and bore people who can not read them. Even scale models and Soane's spidery drawings have limited appeal; nothing beats actually stepping inside a building. You need to engage all the senses in learning to love an architect, discovering whether the building is cold or warm, its smell, the way the light falls, whether it is awe- inspiring or intimate.

With the Soane Museum just down the road in Bloomsbury playing to packed tours, making the exhibition as atmospheric as Soane's magical mystery tour was as challenging as staging Phantom of the Opera without dry ice. Worse, many of the architectural perspectives are watercolours which fade under high levels of light, so the four galleries in the RA are purposefully dimmed down. The exhibition's designer, Piers Gough of CZWG, used those dimmer light levels to create pools of light in a rather Soanian way. He also decided to show us how Soane manipulates both space and light by building replicas of the domes at Lincoln's Inn Fields to demonstrate how they wrap around entire rooms to become the walls.

Soane's pendentive domes, outstretched like bats' wings pinioned to the corners of the room, turn the ceilings into membranous shelters. It was Philip Johnson who declared that John Soane was "really a ceiling architect. That's not trying to make him look small. When you think of one's actual experience of ceilings, you mean wall, ceiling, enclosure and light."

Setting up this exhibition of Soane's coolly elegant, honed-down classicism in the RA was no mean feat as its architecture enshrines precisely the aesthetic Soane rejected. "Frankly it would have been easier to do it in the Hayward," Gough admits. "Fighting the overblown boudoir classicism under those vast cornices was very un-Soane-like." Gough's strong structural installations reduce the impact of the RA to offer us axial routes and vistas as seductive as Soane's.

Then Gough lets us join the Magic Circle to find out what makes Soanian tricks work, and banish Soane's epitaph - "picturesque" - forever. This fantastic precursor of so much of modern architecture is revealed with all the tricks and illusions that traditional Beaux Arts-trained architects, with their love of architectural neo-classicism, ignored and put Soane out of fashion. Looking up into one of Gough's sectional ceilings - modelled exactly on Soane - you can see the lanterns that beam light down through three floors cut up with the walkways in Soane's own home. To warm up the grey northerly light Soane lined these lanterns with amber glass and painted his breakfast room a zingy yellow. Mirrors pasted in the most unlikely places - the back of pictures or bulbous eyes on doors - bounce back light and Gough has hung one of the doors from the museum at the RA. By the time the light filters into the basement, where Soane housed a sarcophagus, the atmosphere is faintly spooky - "morbid, very fin de siecle," says Gough. Like any capricious impresario of special effects, Soane cancelled visits on dull and rainy days.

A carriage clock chiming sweetly on the hour at the RA takes us straight back to Soane as a young man. On the wall, his diary entry for 18 March 1778 reads: "At five in the morning set out for Italy." That Grand Tour began a love affair with antiquities and the classical orders that never ended. Here are the Piranesi drawings that Soane displays so ingeniously on pull-out rods in his picture gallery at home, and a huge canvas painted by his fishing partner, JW Turner, that Soane commissioned for his house but sent back as he didn't like it, now on loan from the Tate. His early interest in Primitivism, creating Greek temples out of tree trunks is there, plus drawings and models of Tendring Hall in Suffolk, Saxlingham Rectory and Tyningham in Buckinghamshire, to remind us that Soane designed 18 new country houses early in his career.

His strong adherence to symmetry and interest in light and shade, and his simplicity and precision in handling brick and stone are revealed in photographs, models and architectural elevations of these houses, alongside a dictum from Abbe Langier whose essay on architecture, translated in 1755, informed Soane: "An artist ought to give a reason for everything he does." Hanging on the walls in this gallery are Joseph Gandy's architectural perspectives of Soane's work. From 1798 we see his work in a new light, as Gandy introduced atmospheric skies, exaggerating the scale of the buildings under thunderous clouds.

Moving on through the gallery to Soane's mature work: the Dulwich Picture Gallery of 1811-12, and, as clerk of works between 1807-1837 at the Royal Hospital in Chelsea, his stables with brick arched openings established his minimalist style. A fascinating on-screen walk through the banking halls at the Bank of England, Soane's masterpiece that introduces him as Britain's first minimalist, has been made possible by projecting Frank Yerbury's b&w photographs of the bank on screen. They reveal its austere monumentality and crisply chiselled lines.

Soane's observation that "mouldings are as essential and important to an architect as colours to the painter" is printed next to the boldest dome of his career - the banking hall where he all but removed the walls and placed most of the dome on the floor so bankers stood in a hemispherical space. The Edwardians demolished the Bank to replace it with a pedestrian block by Herbert Baker. As the Soane museum curators observe ironically: "The Napoleonic wars built the bank: the First World War destroyed it."

The final gallery, painted red, is "about the madness of the artist", Gough explains. "Most of it is incredible. Here lies the processional route that Soane planned for King George IV from Windsor Castle to Buckingham Palace, together with the plaintive letters seeking to show the monarch his drawings. Designed to appeal to George IV's taste for pageantry, opulence and military symbols, it never won favour but Soane did get to design the royal entrance to the House of Lords, its pavilion decorated with Britannia in a chariot.

Wrapping classicism around a medieval hall and exploiting its buttresses like this was an extraordinary feat for a classicist, but alas, it burnt down in 1834.

Joining the Freemasons, his designs for their Council Chamber between 1813 and 1831 reveal a dome designed to resemble a canopy suspended from the ceiling with no apparent support. Soane's dissolution of structural conventions and use of mysterious lighting from a lantern of stained glass with all the zodiac signs is the architect at his most mystical. Piers Gough admires it: "This skill of being brilliantly theatrical with light and form and space has been largely lost in the freedom of modern architecture."

Gough has replicated Soane's tomb in a St Pancras churchyard and in the process restored it to its former glory. The real tomb has been vandalised, its marble pillars removed and stonework scorched. Designed by Soane as his wife's vault, it attracted his first admirer, Sir Giles Gilbert Scott, who used its silhouette to design K2, the telephone box that sprung up all over Britain. Camden council has miserably failed to restore the Grade 1 listed tomb despite being offered cash from the Heritage Lottery Fund in 1997. Perhaps they'll be shamed into action by this final tribute from Piers Gough at the Royal Academy. It would indeed be sad (or SAD?) if they failed to do so.

`John Soane: Master of Light and Space', the Royal Academy of Arts, London SW1, to 2 December. Tickets: 0171-413 1717