Originally built in 1914 for the 1915–16 Panama-California Exposition, the Cabrillo Bridge is the main gateway to San Diego’s Balboa Park. For the park’s centennial in 2015, the spandrel-style concrete structure, which measures 769 feet long, underwent a major rehabilitation and seismic retrofit as part of a collaboration between the city and the California Department of Transportation that included a lighting treatment.
Engineering firm CH2M was hired to oversee the lighting; the company, in turn, called on Faith Baum, principal at New Jersey–based Illumination Arts (IA), a lighting design firm known for its expertise with bridges. Baum and IA’s senior designer Elizabeth Johnson embraced the challenges of the project brief and the site—the bridge crosses Cabrillo Canyon, along which runs state Route 163, host to more than 100,000 vehicles a day.
One of the more unusual aspects of the project was that the stakeholders already had an idea of how they wanted the bridge, which is listed on the National Register of Historic Places, to be illuminated: They wanted its façade lit. Baum and Johnson were quick to point out that this wasn’t the only possibility, and doing so would make the bridge appear flat. Using renderings and an elaborate on-site mock-up, the lighting designers showed that they could achieve the client’s desired effect by lighting the undersides of the seven 46-foot-wide arches rather than the bridge face. Lighting the arches would give dimensionality to the structure and its 14 piers, which vary from 60 to 129 feet tall, without interfering with the freeway below or the existing 70W high-pressure sodium streetlights on the bridge above (neither of which were part of the project scope).
Bridges are one of the few project types that have been ahead of the curve in using LEDs, Baum says. When this project commenced in the summer of 2012, “The [LED] technology we had at the time was ready to do this project,” Johnson says.
The lighting strategy employs a single fixture type, a spotlight, but in two different sizes: 140W for the primary extra-large fixture and 50W for the smaller fixture used at the bridge’s end piers. The mock-up determined a client-preferred color temperature of 3000K. A precise linear spread lens aligns the fixture’s elongated beam with each pier leg. Pairs of fixtures sit at the base of each leg to achieve the cross-lighting effect.
As is often the case with complicated lighting projects that appear to have a simple solution, a tremendous amount of behind the scenes work and coordination was involved. Because IA was not going to be on-site for the fixture aiming, Johnson spent a significant amount of time documenting the aiming points for the engineers. She determined the vertical and horizontal tilt for each luminaire so that they would all hit the correct locations on each arch. The slope of the site required a range of vertical aiming angles—from 123 degrees at the shallowest point to 150 degrees at the steepest. And adding to the complexity were the jogging paths that run along the slopes of the canyon. To prevent fixture tampering and to avoid blinding joggers, the designers built a custom concrete enclosure with a cover grate.
Surprisingly, this was the first time the bridge had been lit for aesthetic purposes. The lighting design successfully celebrates the structural form and enhances its nighttime appearance, all while furthering the landmark’s significance for the local community. •
Project: Cabrillo Bridge, San Diego • Client: City of San Diego partnering with California Department of Transportation (CALTRANS) • Original Architect: Thomas P. Hunter (bridge built in 1914) • Engineer (lighting): CH2M, San Diego • Engineer (seismic retrofit): T.Y. LIN International, San Diego office • Lighting Designer: Illumination Arts, Bloomfield, N.J. • Project Size: The spandrel-style concrete bridge has seven 46-foot-wide arches, 14 hollow piers, and measures 769 feet long • Project Cost: $23 million • Lighting Cost: $200,000 • Code Compliance and Watts per Square Foot: Not Applicable
Lumenpulse: Lumenbeam large and extra-large fixtures used throughout with a narrow-spot beam spread and a linear spread lens