challenge Glasgow has joined the ranks of European cities employing light as a vehicle for urban design and civic renewal. The City Council's lighting initiative-'Glasgow: City of Light'-not only complements the municipality's extensive rejuvenation plan for the neglected stretch of land on either side of the River Clyde, but extends to encompass the city in its entirety. While the initiative aims to revive the Clyde's social, economic, and physical map, where industrial areas that once thrived from shipbuilding now sit derelict after the industry's decline, it also hopes to develop lighting as a recognizable art form in the city.

architectural and lighting solution With a topography populated by church spires, prominent landmarks, and bridges, Glasgow's architectural assets are receiving dramatic makeovers with light. One project recently completed in the second phase of the city's proposed three-phase lighting strategy is 'Chroma Streams; Tide and Traffic' on the Kingston Bridge, an installation by lighting design firm Leni Schwendinger Light Projects. Commissioned by the Council, the project explores the interplay between the traffic flow on the bridge and the slow change of the river's tides.

As the busiest road bridge in Europe, carrying over 180,000 vehicles a day, the Kingston Bridge comprises five traffic lanes in each direction, supported by two monumental concrete arcs. A 'big beast in urban terms,' says Ian Alexander of JM Architects, who collaborated on the project, 'but with a certain unadorned elegance.' In order to design the lighting, Leni Schwendinger, founder of Light Projects, looked to the underside of the bridge, an aspect of the structure she really loved, as inspiration. And then an idea presented itself: 'It came to me one day that there were two great flows,' Schwendinger explains, 'the flow of the traffic and the flow of the river.' While researching the Clyde, she happened upon physicist Lord Kelvin's tidal graphs, which prompted the consideration of how these flows could be measured and illustrated through color on the bridge itself.

Providing a daytime element to the installation's nighttime presence was important to the design. Four 20-foot-tall stainless-steel sculptural armatures, inspired by Lord Kelvin's curvy nineteenth-century graphs, were planted in pairs on each side of the river. Three color-changing washlights fixed on each stem are fitted with custom barndoors to help direct the light upward, recreating the swoop of the bridge's underside, and 575W metal halide lamps provide all of the illumination. For a design that was seemingly simple, 'it took night after night of adjustments to finalize the focus,' explains Schwendinger. 'It was the most arduous focus I've ever done.'

The colors projected onto the bridge are the result of highly orchestrated programming that allows for 144 sequences derived from the real-time patterns of traffic and tide. Because the tides are a predictable condition, a linear mutable color pattern starting at the cool end of the spectrum-from light green to indigo blue-was assigned to illustrate their four interlocking cycles. The variable flow of traffic is based on levels of service, measured by volume and speed. Like a grading scale, the best traffic (A) is yellow, meaning constant and clear, while the worst (F) is red/pink, a static traffic jam. Each of these levels represents a color on the warm end of the spectrum. Each minute, data is transmitted from streetlight sensors and sent to a 'black box,' where it is translated into a preprogrammed scene. 'We wanted the transitions to look pleasing and intentional' explains Schwendinger. 'Even though it's shown in real time, it's not changing in a non-disciplined way.'

With this installation, the Kingston Bridge has become an interactive artwork physically depicting the city's rhythms and providing users a gauge for what to expect on the road ahead. The lighting strategy allows the familiar to be viewed in an artistic context, in this case, says Alexander, 're-engaging and modifying a perhaps poor perception of the bridge in the public eye.' sallie moffat