The lighting program for the Seattle Public Library offers a model for efficiently illuminating a building dedicated to the experience of engaging books.

» The new $165 million central branch of the Seattle Public Library, designed by the Office of Metropolitan Architecture (OMA) with Seattle's LMN Architects, in a joint venture, is garnering worldwide attention for its striking 11-story glass form.

Rising on the site where two previous and much smaller central branches stood, this nearly 363,000-square-foot structure, the hub of Seattle's 26-library network, consists of five platforms that OMA pushed and pulled to the site's boundary. This design, which produced irregular ceilings heights, proved a challenge to its lighting designer, Manhattan's Kugler Tillotson Associates (KTA), and demanded out-of-the-ordinary applications for conventional materials.

OMA was selected after an intensive open request for qualifications and interview process, which also included the notable firms of Norman Foster, Cesar Pelli, and Steven Holl. OMA was selected for the project because of its ability to design bold structures with impressive acoustics and finishes on very low budgets, recalls library head Deborah Jacobs. 'More than design ability, the library wanted an architect,' Jacobs continues, 'who didn't have the answers, but who had the intelligence for approaching the answers.'

Working in close collaboration with KTA, who also designed the lighting for OMA's Prada Guggenheim store in New York City, OMA and LMN created a building with a cost- and energy-efficient lighting design comprised of three elements: a custom-crafted metal-mesh curtain-wall glazing, a system of dot and strip fixtures, and an arrangement of reflectors and directional lighting. The team chose these solutions in response to the facilities program, architectural design, tight construction budget ($272 per square foot), and Seattle's strict municipal energy codes (1.5 watts per square foot for general library areas; 1 watt in the three-story auditorium; and 0.2 watts for the 143-vehicle underground garage). KTA's lighting challenge was intensified by OMA's directive that prohibited attaching lighting fixtures to both the exterior and interior faces of the curtain wall.

Metal Glass

To clad the curtain wall that encloses the reading and heavily trafficked public areas, OMA/LMN developed a triple-layer glazing system. Embedded with a curved aluminum mesh in the outer air cavity and filled with krypton gas in the inner, OMA partner Joshua Ramus-a Seattle native and OMA's principal-in-charge-calls it Metal Glass. Custom-manufactured by the German firm Okalux, it strategically covers approximately 50 percent of the building, while a standard double-layer glazing system encloses the other 50 percent. This glazing minimizes glare and diffuses direct wavelengths, which in turn reduces thermal transmittance, improves UV value, lowers solar heat gain, and lessens the use of cooling systems. Metal Glass is similar to a tint coating, except that it only filters non-visible wavelengths. To maximize the performance of the Metal Glass and double-layer glazing, OMA/LMN added an extremely high-efficiency, low-e coating.

The design scheme also includes a 40-foot-square skylit atrium to channel more daylight into the interior. As a result of the structural design, the building is sculpted to maximize daylighting opportunities in communal areas like the 'living room' and the reading room (on the third and tenth levels, respectively), and the designers positioned heavy-use spaces (i.e., book stacks and meeting rooms) in areas shaded from daylight, further minimizing heat gain and eliminates glare on the monitors of the 400 computers for public use. OMA's daylighting system set the stage for KTA's electrical lighting solution.

Dots and Lines

KTA was an obvious choice for the library's lighting design. With a recommendation from OMA and after an intensive interview with the library's board, KTA won the project because of its experience lighting libraries. Former principal Suzan Tillotson, who recently opened her own firm, Tillotson Design Associates, has 35 libraries in her portfolio. From the beginning, Tillotson strove to accommodate the library's desire for a warm and inviting atmosphere and its need for adequate illumination, particularly in the book stacks. The lighting system needed to support the regular operations of the library's nearly 330 employees, while serving the diverse activities of the institution's anticipated 8,000 daily visitors-double the number of visitors to the previous central branch. Further complicating these challenges, KTA was charged with illuminating spaces configured with ceilings ranging in height from 8 feet to 50 feet, while complying with Seattle's strict energy codes. KTA's response was to go with the basics: dots and lines.

Tillotson began by studying models that showed the interior's quality and quantity of natural light. Armed with this information, she created a map to evaluate how changes in sunlight, by hour and season, would affect the interior atmosphere. Both KTA and OMA wanted to use dots (points of light) for the lower levels, and two types were selected: luminous pendants and recessed fixtures. These fixtures accommodate the building's varying-shaped structural modules. For the first-floor children's section (image right), where the ceiling ranges from 8 feet to 16 feet, Tillotson designed single-bulb acrylic pendants alternately lit with 55W and 85W Philips QL induction lamps. She explains that this source, enhanced by the use of reflectors, 'provides an abundance of functional light without exceeding code.' For the building's upper levels, such as the four-story switchback-slope spiral-stack area (where the library's 1.4 million non-fiction collection is organized in a seamless Dewey Run), Tillotson selected 4-foot-long, double-lamp T8 striplights.

Arranged perpendicularly to the site's steep slope to create a flattering exterior visual of the building at night, the inexpensive fluorescent striplights are hung in the stacks above a polycarbonate ceiling plane, which OMA also used in its design for the Prada Guggenheim store. Sam Miller of LMN explains that the polycarbonate diffuses light evenly without producing shadows and provides enough illumination for visitors to view books on the bottom shelves. The selected metal halide fixtures have perforated metal screens that offer transmissions of 20 percent, 60 percent, and 80 percent. In some areas, where these lights are hung above perforated and corrugated metal ceiling planes, KTA calculated the light loss to create a light pattern that Tillotson says, 'provides ample and functional puddles of light.' The budget prevented KTA from using dimmers; instead, occupancy sensors conserve electricity in low-use areas, such as the special collection section. KTA also backlit the eye-popping chartreuse escalators and elevator cabs to enhance the building's wayfinding system, which includes, in lieu of navigational signs, the hierarchy of dots on the public floors and lines on the non-public floors.

Directional Lighting

Lighting the glass-ceiling reading room proved KTA's greatest challenge. OMA prohibited KTA from attaching lighting fixtures to the diamond-grid curtain wall on both the interior and exterior of the building. Tillotson's solution utilizes task lighting on the desks and uplight floor luminaires-both designed by KTA and manufactured by Vitra-that emit light on all four sides in the seating areas. Lit from within, and without employing exterior structural illumination of any kind, the library reads as a beacon at night. Interior lights on the lower levels are positioned outward to illuminate the building's immediate exterior perimeter.

KTA used common yet effective sources and materials-Philips QLs, metal halides, and reflectors-to provide a solution that is economically efficient to maintain. (Because the structure's atypical design includes interior cantilevered spaces, OMA/LMN developed a maintenance access plan that enables the library to easily replace bulbs and service fixtures.) Perhaps even more important, Miller notes, is that the lighting design stands as an example of Tillotson's appreciation for the library's criteria: a practical lighting solution, inexpensive and easy to service, that amply illuminates the interior with a friendly and inviting warmth. Together, the lighting design and the architecture it illuminates have created a thriving urban center that is fast becoming an integral part of the city's culture. Joseph Dennis Kelly III