A tubular unit called a "soffitto," constructed of glass-fiber-reinforced gypsum diffuses and directs light into the galleries.
Arup Lighting A tubular unit called a "soffitto," constructed of glass-fiber-reinforced gypsum diffuses and directs light into the galleries.
The High Museum in Atlanta.
High Museum of Art / Jonathan Hillyer The High Museum in Atlanta.

Architect Renzo Piano has a way with light. It is what has kept museum directors and trustees beating a path to his offices in Paris and Genoa since the 1987 opening of The Menil Collection in Houston. "Every time you take a new job, the one thing that's constant is the magic of light," Piano says. "But everything else is different—the direction of sun, the energy consumed, the people you are working with." Except, that is, for the engineers and lighting designers of Arup—who have been collaborating with the Renzo Piano Building Workshop (RPBW) on an extraordinary series of museums across the United States (not to mention elsewherein the world) for almost 30 years. These projects, which include newly completed or under construction projects in Dallas, Atlanta, New York, Los Angeles, and Chicago, redefine the use and perception of natural light in a stunning array of subtly different essays on this eternal theme. London-based Arup Lighting Associate Director Arfon Davies has been a key member of the team for the past 10 years encompassing all of the recent American projects. He classifies museums into two schools of thought: a European approach that uses diffuse natural light to fill the room and a more dramatic American approach that stresses a lot of  contrast with electric lighting focused on individual objects. "Renzo has brought this European attitude to America," Davies says.

Another distinct attitude that Piano brings to each project is that of a builder. He often cites his pedigree from a family of builders in Italy. "Architecture is about dreaming, history, memory, sociology, poetry," Piano says. "But at the end of the day, construction is the fundamental experience of architecture." Since making things, particularly things as complex as buildings, seldom is a solitary venture, Piano embraces the input of others as thef oundation of a collaborative process. "However cryptic the first sketches are," says Arup's Davies, "they already indicate a direction or solution that isinformed by a deep understanding of how light enters and is distributedt hrough a space". This first stage of the design process involves many exchanges and iterations between RPBW and Arup which refine and sometimes redefine the approach. "These early stages of the design process can be very intensive as we strive to balance the many aesthetic and functional requirements," Davies says.

The initial design investigations are dubbed the workshop phase and include all the project consultants and clients. This establishes the basic goals and directions for each project. "It's making things that make sense," Piano says. The continuous dialogue is essential to Piano's process."I could never invent a shape or a solution and then ask the engineer if it's possible,"he says.

Each RPBW/Arup museum is a variation on a single theme: developing some reflecting, refracting, or otherwise obscuring element that shades a roof structure from direct sunlight. These features demonstrate Davies' assertion that "lighting can really form the shape of a building." Piano notes that it always begins with the basic geography of each site and the directional needs of natural lighting in museums—unfiltered northern light and varying degrees of shading for east, south, and west. While almost every American city is laid out on a grid, north is not always north. While Chicago's Art Institute is perfectly aligned with the compass ("Chicago was built on a map made by a military topographer," Piano notes. Houston's grid is off by a few degrees. It is even trickier in places such as Dallas and Atlanta where the projects are in locales that are not set on the orthogonal. At the High Museum in Atlanta, the roof is composed of 1,000 individual skylights that Piano likens to a field of sunflowers. "It's actually the opposite, a sunflower looks for light from the south; we're looking for the north," Piano says.

The High's roof is probably the ultimate demonstration of the complex interaction between RPBW and Arup. The shape began with Piano's metaphoric flowerand initially was developed through a series of small and eventually full-scalemodels, a particular strength of Piano's office that Davies cites as crucial to the continuous dialogue between the architects, engineers, lighting designers, and owners. "The part and full scale models allowed us to investigate the distribution and quality of light and how it was affected by changes in geometry and finishes," Davies says. "Mock-ups provide an invaluable tool to enable us to communicate and explain the design approach to our clients." Arup's detailed analysis was not just confined to illuminance levels. The circular skylights are configured in a gridded ceiling that is designed to reduce clutter. Arup's integrated approach to all its engineering services resulted in structure, electrical lighting, and even the fire sprinklers effortlessly recessed within the sculpted natural lighting system.

Piano and Arup's design for the Art Institute of Chicago's Modern Wing is scheduled to open next year. A carpet-like metal screen structure floats above the galleries' glazed roof. The elaborate fins that provide shading are close in spirit to the Menil Collection because of the similarities in north-south siting. By contrast, the Nasher Sculpture Center in Dallas has a very different quality of light driven by both its function and its orientation. Where a painting gallery at the Art Institute is limited to about 25 foot-candles of acceptable light, the Nasher is a venue for sculpture and can utilize a dramatically brighter 100 foot-candles of natural light. Even so, the intensely bright Texas sun needs considerable filtering to achieve this level, and the site's deviation from the compass required a solution that shares some similarities with the High Museum. Arup's innovation here was developing the optics for a cast aluminum screen composed of many thousands of "solar bracelets" that redistribute the light through a curved glass roof above each gallery. These elements create an ideal geometry that excludes sunlight when necessary.

The next step in RPBW and Arup's evolving collaboration is an addition to Louis Kahn's iconic Kimball Art Museum in Fort Worth, Texas. The goal is to create a carbon neutral building that provides a model for sustainable building in a museum. "It's almost an impossible task to have good natural light without entrapping the heat gain of the sun inside the building," Piano says. One key difference in the design is an effort to optimize the quantity of glass on the roof, both to reduce solar gain and maximize surface area for photovoltaic cells that can provide energy for the building. Arup's engineers conducted an optimization study for the building and determined that electrical lighting is the major consumer of energy within a museum (and hence the major contributor of carbon emissions). Thus, the goal is to keep the electrical lighting off as much as possible. This requires maximizing the natural light within galleries." It's the approach we've always taken, but now it's an even more important aspect of design since it allows you to switch off the electric lighting and make substantial carbon reductions," Davies says. 

Despite winning the 1998 Pritzker Prize and the most recent AIA Gold Medal, Piano's dedication to a collaborative approach is genuine. "If you ask me who did this or that I'm not going to be able to tell you," he says. He describes his long-standing relationship with Arup's engineers as a team of good explorers who work hard to develop new ideas in every project. "The curiosity and desire to explore new ground is great," he says. Many museumgoers will agree that the results are as well.

Edward Keegan is a Chicago architect who complements his independent practice by writing, broadcasting, and teaching on architectural subjects.