Let there be light

Salisbury Cathedral, one of Britain’s finest examples of medieval architecture, is celebrating its 750th birthday in style with a spectacular lighting makeover. But with exposed cabling a serious no-no and ceilings stretching up higher than heaven itself, what of the poor contractor who takes up the gauntlet?

The £800 000 contract brought with it a range of challenges from the outset for electrical contractor RT Harris. Project manager Andy Weeks had trouble finding electricians who were skilled in mineral insulated cable terminations.

“It always presents a problem, as it seems to be a dying trade,” he says. “We persevered, but then another difficulty is that RT Harris does an awful lot of MIC work because we’re involved with the Oxford colleges. Although we have a fair number of people who can do it, finding them available is another matter.”

Another major challenge for the Oxford-based contractor was getting a new sub-main from the lower levels into the Cathedral’s imposing clock tower. Weeks came up with an innovative solution.

“We had to go onto the outside of the building, find a corner which is not exposed to the public eye and use steeple jacks to install cables onto the wall. So that was novel,” he says.

Despite such challenges, Weeks has the kind of enviable attitude which suggests he takes everything in his stride.

“It’s always a problem when you get ancient monuments. You can’t drill holes where you want to, nobody wants to see cables, so you have to find routes where you can hide them. But you just have to try your best on it and try not to destroy the fabric of the building.”

Light + Design’s Jim Morse, who designed the scheme, explains that there are three cornerstones to the ambitious design: “First and foremost, the lighting had to show off the Cathedral’s magnificent architectural features to their best advantage. Secondly, we had to significantly reduce energy use. Thirdly, we had to minimise light pollution.”

The designer has certainly achieved his goals. Energy use has been reduced from 20kW to approximately 13kW, and the finer points of the architectural design are enjoying a new clarity since the banishment of brutal mid-eighties dimmable fluorescents.

Morse’s interior concept consists of three principal elements. From the high clerestory level, 575W ETC Source Four PAR wash lights illuminate the nave. The fully dimmable product has excellent colour rendering and long throws.

The second main component is the Cathedral’s uplighting. This is provided by Norka’s 1-10V dimmable linear fluorescent sources with a colour temperature of 2700K. Although the product was designed for outdoor use, it is ideal for the cavernous interior. Its fluorescent tube is an accurate parabolic reflector, resulting in excellent control.

Norka fittings also light up the space from the window sills upwards, where concealing modern technology is vital.

“We got enough light off the side aisle vaults and we didn’t have to have any supplementary downlighting at all. We could bring one cable down in a very discreet position and run along the window sills to all the luminaires along the side aisle,” says Weeks.

One of the few places within which lighting is visable is the crossing. When the spire was erected over 100 years after the building, extra weight on the crossing columns meant buttresses had to be added, including a stone bridge which offers a perfect lighting position.

Here Weeks’ team has installed what amounts to a technician’s gallery, comprising horizontal outrigger lighting bars and a matrix of stage lighting sockets. If Metallica fancies performing a gig within this ecclesiastical tour de force, there will certainly be no objections from a technical standpoint.

The entire lighting system is controlled from a single panel, massively simplifying the previous controls. Inspired by St Paul’s Cathedral, Light + Design specified the sophisticated Lutron control system, which allows the user to create a flexible range of effects and enables various sections of the cathedral to be illuminated at any one time. Hand-held lighting controllers can also be plugged in to additional locations.

Since the 1960s, the exterior of Salisbury Cathedral had been lit by 2kW floodlights, positioned in pits up to 50m from the building. The effect washed out much of the fine architectural detail and led to a great deal of waste. Whilst some light hit the building, a huge amount also careered off into the night sky.

The revamp sees outdoor lighting brought much closer to the Cathedral walls, with 70W Meyer Superlight floods targeting individual areas.

The stunning internal installation took about 12 months, but RT Harris is yet to complete the ambitious project. “There’s still scaffolding on the exterior and it will be 18 months before we can do the final touches,” says Weeks. “But we’ll be delighted to go down and finish it off. It’ll be great to see it in its full glory.”