Located at the confluence of the Sacramento and American Rivers, and cradled in Northern California’s Central Valley, Sacramento is a city of agriculture, undulating vistas, West Coast sun, and, perhaps, most importantly, trees. While exploring the city in 2005, architect Brent Kelley, principal of Corgan Associates, understood how the place earned the moniker City of Trees. “You get these large canopies overhead and the sun filters down creating a dynamic of shadow and light,” he says.

It was this interplay of light that inspired the design for the new Sacramento International Airport, designed by Corgan with Fentress Architects and completed in October 2011. The city had been in desperate need of an airport upgrade and wanted a building worthy of being located in the state’s capital and capable of luring travelers away from nearby airports, such as Oakland and San Francisco. “They were looking to make a statement—what they referred to as an iconic structure—that would be associated with Sacramento,” Kelley says.

Corgan and Fentress designed two structures, a new terminal (landside) building and a 19-gate (airside) concourse connected by a train shuttle system. Allowing natural light to filter in, as well as allowing views out to the city and distant mountains, became the central design goal, and the architects proposed a sweeping terminal building with three-story, canted glass curtainwalls and clerestory windows. The design was initially met with skepticism. “When we first presented the building, one of the members of the board of supervisors said, ‘You’re obviously not from Sacramento if you’re proposing a glass building.’ It took a lot of convincing,” Kelley says.

The conviction that a building with east, west, and south facing glass walls could earn LEED status, meet California energy codes, and not overheat or blind its users was achieved, in large part, through the careful analysis and lighting design of Arup. The firm joined the design team in 2007 to execute electric and daylighting design for both of the buildings. The architects had already designed an exterior sunshading system of louvers meant to protect against heat gain and glare, and they asked Arup to assess the design with lighting in mind. “Our starting point was this big glass box and our goal was to make the space feel daylit, but to make it visually comfortable,” says Jake Wayne, senior consultant in lighting for Arup, who is based in their San Francisco office.

How then do you take advantage of the benefits that the California sun provides while also controlling it? Arup conducted extensive analyses of the daylighting attributes of the site and how the sunlight would interact with the building through the proposed shading design. “The architects built a very detailed 3D model,” Wayne says. “We could take that and bring it into Radiance and run a series of simulations for winter solstice, summer solstice, and the equinox.”

Initially, the client and the architects had concerns about Sacramento’s intense summers and how to mitigate heat gain, but Arup’s investigation revealed a different challenge: the low-in-the-sky winter sun. In winter months, the sun doesn’t rise above 40 degrees and the study showed how light would pierce the gaps in the exterior louvers from mid-morning to late afternoon, effectively blinding the airport employees working at the ticket counters. “Everyone thinks ‘summer’ when you think about the sun and the heat, but it really is the winter sun that plays the biggest role,” Kelley says.

Arup’s findings led to a redesign of the exterior louvers. “In school, most architects are taught that when you want to protect an east and west façade then you go with a vertically oriented sunshade,” says Mark Outman, associate principal at Fentress. “We learned from Arup that the horizontal shades work much better.”

After multiple mock-ups using a variety of materials, the louvers were fabricated out of perforated metal and attached to the exterior mullions at specific angles based on Arup’s data. The result was exactly what the architects envisioned. “You still get views out, you still see sky, and you get this wonderful, dappled daylight in the space that changes throughout the day,” Outman says. The natural light is so prevalent that electric lights are only required in the evening.

But the use of light—natural or electric—throughout the project is more than just atmospheric. In the terminal (landside) building, it serves as the central wayfinding tool. The architects created a central spine that attracts travelers as they enter from the curbside drop-off. “You gravitate to the center of the building and move along this axis of natural light,” Outman says. Once inside, visitors encounter a majestic glass-and-steel space capped by a wood ceiling constructed, in part, with redwood reclaimed from a pedestrian bridge in Sacramento. This gives the building the appearance of a tree-lined street.

Minimal electric light supports the wayfinding. A concentrated amount of illumination at the ticket counters, which are treated like linear kiosks with an LED backlit lightbox as a header, is mimicked at the train platform that takes passengers to the concourse building. “We wanted to create a hierarchy of light,” Wayne says. “You enter the ticket hall and see the glowing ticket counter. You go up the escalator and you find the train by looking for the glow at the loading stations.”

At night, electric light is used judiciously to prolong the radiance that the building has during the day. Arup lit the redwood ceiling in the ticket hall using 315W T9 ceramic metal halide asymmetric uplights surface-mounted on the square structural columns. A line of 150W T6 ceramic metal halide downlights accent the center band of each ceiling bay. Arup also supported the airport’s $8 million public art program by working with some of the country’s top artists to achieve dramatic effects, such as lighting, with adjustable monopoint fixtures, a 60-foot-tall red sculpture of a rabbit that seems to dive through the main ticket hall.

The interplay of material, light, and surprising architectural form continues in the concourse building. Once passengers make it through security, sufficiently well-lit with a combination of 39W T6 downlights and 32W T8 fixtures, they encounter a sweeping, curved ceiling with clerestories on the sides that leads to a food court and the gate areas. The undulating ceiling is composed of wood shingles that appear to be lit from within, thanks to the concealed T8s. A dramatic and ample architectural gesture, the ceiling required a unique lighting treatment. “We were staring at this long ceiling and wondering what we were going to do to light this, and then we thought of using tiled ceiling panels where the light would glow through,” Wayne says.

As with all the elements of this project, Arup wanted to test the proposed design. “We built quarter-scale mock-ups and hung them up in our mail room,” Wayne says. “It was the only place big enough to hold them. Then we invited the architects [to look at them].”

Outman remembers that meeting. “It was a tight space. But that was a creative solution that began as a germ of an idea. And that’s what it takes: You have an idea, you go and test it, if it looks good and works, you move forward,” he says.

In January 2012, Arup had the opportunity to see how all of their analysis, planning, and prototyping turned out. They returned to the airport to conduct a post-occupancy light study, taking time-lapsed photos of the space and comparing them to the 2007 analysis. They wanted to see how well the finished, implemented design matched their calculations. (See video link in Details, below.)“We have a side-by-side video from the entire day to see if there is parity from what we predicted, and you can see that it basically matches,” Wayne says. “The post-occupancy study was one of the most exciting things. This was a [large] building for this kind of in-depth analysis and to see that we were able to pull it off is pretty cool.” The project team’s attention to architectural detail and understanding of light’s nuances has created an airy yet intimate space for air travelers and has given the city of Sacramento a building uniquely its own. •

Project: Sacramento International Airport Central Terminal B, Sacramento, Calif. • Client: Sacramento County Airport System, Sacramento, Calif. • Architect (terminal landside building): Fentress Architects, Denver • Architect (concourse airside building): Corgan Associates, Dallas • Lighting Designer: Arup, San Francisco and New York • Electrical Engineer: The Engineering Enterprise, Alameda, Calif. • Project Size: 669,000 square feet (landside and airside buildings combined) • Project Cost: $1.1 billion total cost • Lighting Cost: $7 million for materials and labor; $10.46 per square foot • Energy Code Compliance: California Title 24 • LEED Certification: Silver • Watts Per Square Foot: Landside: 0.432 (landside building); 0.51 (airside building) • Manufacturers/Applications (only main architectural lighting components): Terminal building: Elliptipar/The Lighting Quotient (315W T9 ceramic metal halide uplights in ticket hall); GE Lumination (surface-mounted LED array for lightbox header at ticket kiosk and train platform); iLight (cove-mounted linear fixture at baggage carousels); Insight (pendant-mounted 54W T5HO luminaire at ticket kiosk); Kramer (compact fluorescent downlights throughout); Targetti (150W T6 ceramic metal halide downlights and 20W to 39W accent lights in ticket hall) • Façade glazing: Solarban (70XL) • Concourse building: Cooper NeoRay (32W T8 linear fluorescents concealed in wooden slatted ceiling); Hess (decorative pole lights at food court); Kirlin (39W T6 6-inch square downlights in concourse)

Video: Watch a video of Arup’s daylight modeling comparison here