Brimming with civic structures, museums, theaters and performance halls, Minnesota's Twin Cities—Minneapolis and St. Paul—are often touted as the cultural center of the heartland. Over the past few decades, virtually every major arts and cultural facility in the two cities have reinforced that notion by expanding their existing facilities or building new ones. Last year alone, the twin towns burnished their reputation as cultural capital of the Midwest with the opening of more than $300-million-worth of new arts and cultural buildings designed by world-class architects.
Among these vibrant new structures is the 353,000-square-foot Minneapolis Central Library, designed by renowned architect Cesar Pelli and his New Haven-based firm Pelli Clarke Pelli. The design of the building transforms the concept of “library” from a staid, inward-looking repository of books to an outward-reaching community center. And thanks in part to its thoughtful lighting scheme; designed by New York-based Cline Bettridge Bernstein Lighting Design, the building truly shines—literally and figuratively.
Located in downtown Minneapolis not far from the Mississippi River between Hennepin Avenue, the city's primary thoroughfare, and Nicollet Mall, its pedestrian shopping street, the glass- and Minnesota limestone-clad library reaches out to the city and draws it in. Its centerpiece is a soaring 5-story atrium topped with a 60-foot-long wing-like zinc canopy. Linking the building's North and South wings, the atrium is flooded with natural light during the day. At night, it glows like a beacon, with the cool light of surface-mounted 4000K metal halide uplights, which bring out the blue tone of its dynamic zinc roof canopy, and the warm light of 3000K ceramic metal halide downlights, softly illuminating the warm-toned surfaces below. The building's alternating wall panels of clear and fritted glass also contribute to the lighting effects, diffusing the light during the day, and permitting views deep into the space at night.
As in the atrium, the lighting throughout the building was developed hand-in-hand with the architecture to meet the needs of a modern library, including the technological advances of the information age. “Libraries are different than they were in the past,” says William Butler, Pelli Clarke Pelli's lead architect on the project. “What used to be an end place for books is today a communications hub, which not only houses bound books, but also offers access to digital information, with librarians navigating an information network.” At the same time, says Butler, current library environments need to operate on two distinct social levels. “On the one hand, a library is a grand civic building that embodies the cultural values of a community—they're much more social than they were before, and serve as centers for community gathering, with spaces for book clubs and lectures. On the other hand, it needs to respond to individuals, with spaces that function on a residential scale, where you can sit down in an easy chair next to a floor lamp, kick off your shoes and curl up with a book. The character and the quality of the light is essential at both these levels.”
From the user's viewpoint, the lighting in the new library had to address the needs of two primary groups—the librarians and the public, according to Francesca Bettridge, principal lighting designer on the project. From an operations standpoint, the lighting had to be flexible, meet strict energy codes, and be executed within an extremely limited budget. “Modern light levels have to be high enough to be comfortable for both aging and young eyes,” says Bettridge. “At the same time we had to meet the state's energy requirements and create lighting in the open stacks and reading areas that could be flexible enough to be moved, if necessary, in the future. So we came up with what we describe as a task/ambient solution.”
The airy, loft-like spaces, which house the reading areas and the open stacks of books in the North wing and the secure compact storage stacks in the South wing, are defined with a grid of mushroom-shaped concrete columns and different colored carpets on each floor. To provide ambient illumination in these areas, the lighting designers created a series of sleek, low-profile rectangular indirect pendant fixtures. Made of white painted-metal and hung from cables from the ceiling, these fixtures contain 54W T5HO fluorescent lamps that reflect off the ceiling and provide an average of 35 footcandles of sustained illumination. In effect, says Bettridge, “The whole ceiling becomes a light fixture offering even, shadow-free ambient light that's very pleasant.”
Over the tall open stacks in these areas, the lighting designers modified the linear indirect pendant fixtures with a custom T-shaped bracket that contains T5 fluorescents in louvered troughs that provide glare-free downlight along the circulation paths on both sides of each book stack as well as a wash of light on the books from top to bottom. (Full-scale mockups of these fixtures were developed and reviewed by a group of exacting librarians before they went into production.) These fixtures are also connected to occupancy sensors and turn on only when the circulation paths are actually being used. Within the adjacent shorter stacks, the lighting designers incorporated hidden 28W T5 fluorescents behind a lip along their upper edges to provide a wash of light on the faces and spines of the books below.
At the reading tables on each floor, the lighting designers provided elegant task fixtures. Reproductions of table lamps seen by Francesca Bettridge at the Royal Library Extenstion in Copenhagen, these sleek fixtures provide a subtle link to the Scandinavian roots of many of the city's residents, and can be controlled individually by the user. With all of the power and data cabling running beneath raised floors, the task lighting is also powered from the floor, making it extremely flexible. “In addition, the fixtures at the perimeter and in the atrium are on photo cells,” says Bettridge, “so when there's a lot of natural light, they automatically turn off to harvest the daylight.” Thanks to these devices, the building uses 30 percent less energy than the minimum required.
Two other areas that received special lighting attention are the Children's Library and what is known as Teen Central, an area created for teens with input from 14 teenage advisers. In the children's section, the lighting designers created a dynamic canopy of light overhead with sunburst-like radial patterns of linear fixtures containing T5 sources. They also introduced shots of vibrant color by nestling LED strips into the branches of abstract tree shapes situated throughout the space. These sources are programmed to provide a kaleidoscope of ever changing colored light over the course of the day. In the teen section, slim T2 lamps, integrated in vertical coves behind diffusers in the millwork of an undulating red wall unit containing books and magazines, accent its sinuous shape. In this area, 37W MR16 track fixtures also punch light onto tables and globe-like pendants of different sizes were fitted with colored bulbs as a fun, slightly irreverent touch.
According to Tom Hysell, a managing principal of the Minneapolis-based Architectural Alliance, the architect of record on the project, the response to the library since it opened has been extraordinary. “One of the first things people talk about when they enter the building is the beautiful sense of light,” he says. Architect William Butler credits the success of the building, and the lighting in particular, with the collaborative approach by all parties of the team from the beginning. “Each reinforced what the other needed all along and the building got stronger and stronger,” he says. “Usually lighting is driven more by utility than by celebratory reasoning, but because the different aspects of this building were accentuated with light, in ways that make each one unique, the entire building feels more glorious.”