Since the opening of Houston's de Menil Collection in 1987, Renzo Piano has produced project after project around the globe that reinforces his reputation as a poet of light. With the opening of the Art Institute of Chicago's Modern Wing in May, the Italian-born architect and his lighting collaborators from Arup are once again riffing on the theme of fins, baffles, and wings that capture and modulate light. Piano fits the new 264,000-square-foot museum addition into Grant Park on the corner of Monroe Street and Columbus Drive, where the site is constricted by a disturbingly awkward 1970s museum addition and an active railroad right-of-way. The Modern Wing provides the Art Institute with a much-needed new entrance from the north with its adjacency to Millennium Park, and a 620-foot-long bridge, also designed by Piano, beckons visitors.

The main artery of the new addition is the two-story-tall, 300-foot-long Griffin Court, which links the new entrance to the older complex of buildings that the Art Institute has built over the past 116 years. This atrium functions as a Great Street. All of the galleries, as well as reception desk, coat check, and gift shop, can be accessed from this dazzlingly bright and airy space. An extensive ground floor education center and the principal new galleries are to the east of Griffin Court. Smaller exhibition areas, for temporary shows and the architecture and design collections, are to the west. Whereas all the art-serving spaces within the new wing provide some elaborately subtle light reflecting and deflecting systems, Griffin Court's simpler roof shades give it a crisp bright light on sunny days that make it a sensory palette cleanser for the visitor who experiences it when transitioning between the different types of galleries in the wing. In the exhibition areas, light is manipulated in the service of art. Within Griffin Court, light simply is. Abundant, bright, clear, and present; the space gives the museum visitor an immediate sense that this is a sanctuary built for light, and it becomes a reference point for both space and light.

In the main portion of the building, the second floor galleries house contemporary art in loft-like spaces that are 16 feet 9 inches tall. They are alternately illuminated by floor-to-ceiling north-facing windows, a small slice of shaded southern light, or ubiquitous tracklighting. All of this is fine, but hardly stellar, given what Piano achieves in the third-floor galleries above.

“Chicago invented modernity in this country,” Piano says. “Steel made the miracle of lightness.” Piano contrasts heaviness and lightness in the volumetric development of the building. The spaces are defined by north-to-south limestone walls that match the material of the Art Institute's iconic Michigan Avenue buildings. But in contrast to the existing masonry material palette, Piano's new icon—the Modern Wing's roof structure—is supported on the thinnest of white steel columns. “This building is solid, but it's also very fragile,” he says. “It's echoing Chicago, not copying.”

This “umbrella for light” provides the sublime illumination for the third-floor galleries that house the Art Institute's extensive collection of 20th century art from the turn of the century through the Second World War. These 15-foot-5-inch-tall galleries provide ample volume for paintings and sculptures of varying sizes. The vellum-lined glass ceiling is a diaphanous layer that is translucent enough to allow views of the roof structure's sculpted wings and fins that reflect Chicago's changing light in a daylong play of light and shadow.

The rooftop sunscreen has become almost a cliché in Renzo Piano's work, but Chicago's Grant Park is an exceptional setting for it. The nearby high-rise buildings contain the homes and offices for thousands of Chicagoans who view the roof as a primary building façade. At 216 feet by 216 feet, the roof overhangs the main body of the Modern Wing by a considerable margin, but Piano dimensions it as a perfect square in order to make a point about the importance of the grid in Chicago's urban and architectural development since the seminal Fire of 1871. “The geography of the place is very important,” says Piano, noting that Chicago's gridiron plan was laid out by a military topographer who held exactly to the orthogonal directions of north, south, east, and west. This precision allowed the architect to plan his building with crisp rectilinear details that work with the symmetrical movement of the sun.

Piano's elaborate light-celebrating roofs tend to get most of the attention in his museums and, at the Modern Wing, the master's handiwork is as compelling as ever. But the one note that was not quite worked out at the building's opening involves another, more traditional, light source—namely windows. The second and third floor galleries feature a double-skinned glass north wall with mechanized shades that permit modulation of light during the late spring and summer months when it is necessary to avoid some direct light from the east and west. Piano intended these windows to provide both light and views, which includes Frank Gehry's Pritzker Pavilion band shell directly across the street and Chicago's stunning skyline beyond. In the early weeks of the building's public debut, the shades were generally found closed to blunt any competition with the museum's art. This is an unfortunate development that will hopefully be remedied in the future. Light in the service of art should not be a simple visual phenomenon; it should engage all the opportunities available to delight and enhance our experience.