TECHNIQUES 6: The slot

Jun 2010 | By Richard Simmonds

The sixth architectural lighting technique championed by Mindseye director Doug James is one of the simplest - the slot

“This is a doozy,” says Doug James of the slot, an architectural lighting technique that has become immensely popular over the past decade.

Although James does not profess to know the exact origins of the technique, he says it is fair to say it grew out of the work of several different people.

“Its origins are clearly in architecture and the use of daylight,” he says. “Architects like Tadao Ando, in his Church of Light in Japan, are using slots to deliver light into a space. At the Kimbell Art Museum in the US by Louis Kahn, there are slots that let light in onto the end wall of the main galleries. He also has a slot that comes in at the top of the barrel vaulted ceiling and reflects light into the space.”

“Architects have been using the technique to channel daylight,” he says, “and then, as is often the case, lighting designers try to find a way to do the same thing with artificial light.”

The slot is similar to the spotlight in a slot described in the first article in this series (December 2009/January 2010 issue) . In this case, however, it incorporates a linear source - typically fluorescent tubes or LEDs.

Two approaches
The diagrams show two variants of the technique. The first is the standard type of installation with square edges and a standard upstand on either side. “That’s fine,” says James, “and if it’s done well with good workmanship there’s nothing wrong with that detail at all.”

An alternative, more advanced, version of the detail incorporates knife-edge profiles for the slot that, when viewed from the ground, reduce the apparent thickness of the ceiling to zero. The top of the trough is curved, eliminating any visual clues to the depth of the slot.

“When you look at a well-done slot with a knife edge and a curved trough, you can’t tell exactly what’s going on,” says James. “You wonder if it’s a panel or a trough.”

“When you look at a well-done slot with a knife edge and a curved trough, you can’t tell exactly what’s going on”

Another variant contains downlights at the top of the slot. The slot delivers visual interest - and perhaps colour - while the downlights take care of more direct illumination. The downside, however, is that a deep ceiling void is necessary to because the architectural detail is the combined depth of the slot and a standard downlight installation.

Applications abound for the slot. It has been used in galleries and in commercial, hotel, retail and residential interiors to deliver practical light into a space without using fittings. It can also be used for wayfinding.

In retail applications, the slot is typically used in circulation spaces, or simply for its visual impact. In galleries, says James, it works well installed around the perimeter of a room so light falls on the walls.

Slotting in - some examples
A good example of this is the White Cube gallery at Masons Yard (pictured) . “The slot is relatively close to the wall,” says James. “Rather than a spotlighting treatment, the philosophy of White Cube is that whatever art is brought in and wherever you place it, it looks good. It’s a very ambient approach to lighting.”

The colour temperature of the light sources is chosen to match the light from the skylight.

At international law firm SJ Berwin, the technique is used to light the circulation spaces that surround a number of atria. James says: “We were able to do that with almost no other downlights - the slot is generating almost all the light for the area.”

“There are linear systems out there that will do something akin to this,” he adds, “but with the slot you can choose how wide it is. This one is about 500mm wide.”

For a refurbishment at the Barbican in London, Mindseye worked with the architects to implement a series of architectural ‘interventions’ for different functions, such as the ticket counter pictured here. “Each one got a line of light as a visual signal, and as a source of practical light,” says James.

Of course, the detail need not be limited to the ceiling. At the Rotunda in Birmingham, there is a sloping entrance ramp with an integrated handrail built into an illuminated slot in the wall.

Pitfalls
The technique may be one of the simplest architectural lighting techniques, but there still pitfalls for the unwary.

“On the face of it it’s a simple thing to do,” says James, “but it’s the detailing that makes it work really well.” First, he says, lighting designers should keep a close eye on contractors. “If you’re not using a system product to create the two edges of the slot, you do have to be on top of the contractor. Often often they’ll design the detail on site and put some structure in to support it which would mean that the lighting equipment could be pushed up above the line of the upstand.”

Also, he cautions that contractors will often assume that only the visible parts of the installation need to be finished to a high standard. “They will paint the inside of the top of the slot and maybe even the sides, but they won’t bother painting out any of the other internal surfaces. That can be a problem if they are using Firestop plasterboard because it’s pink, or coloured plasterboard.”

Finally, he says: “Make sure they get the sequence of works right, because I’ve seen equipment that’s been laid into these things and then they’ve plastered the slot above - dust and blobs of plaster everywhere.”

But the slot is an architectural lighting technique that was born of modern construction methods - specifically the plasterboard linings inside modern building shells.

“It works well in a modern environment,” says James, “but not so well in a 16th century farmhouse… although we are doing a project right now in a 16th century farmhouse and funnily enough, we are using a slot. In a strange way it is less obtrusive than dangling lights between the beams…”