» After an extensive renovation to its original building was completed in 2003 to correct an excess of natural light and sunlight penetration into the galleries, AtlantaÆs High Museum was particularly conscious of the daylighting design for its new addition. Designed by Renzo Piano Building Workshop (RPBW), in collaboration with Lord, Aeck, Sargent Architecture of Atlanta, the two new buildings, which have added 177,000 square feet to the museumÆs original 135,000, exemplify painstaking investigation. The trouble-shooting process involved much computer analysis and an elaborate series of mockupsùfrom a part-scale model at RPBWÆs office in Italy, to a full-scale mockup at a location outside of Atlanta. Though often a budgetary luxury, ôfull-scale mockups are invaluable to understanding the quality and distribution of natural light,ö says Arfon Davies, an associate with Arup Lighting, which worked on both the expansion and the renovation. On this project, the full-scale investigation helped uncover that the geometry of the ôtransition panel,ö which wraps around onto the roof, was allowing direct light into the gallery during the summer months. A custom frit pattern was applied to the susceptible area of the skylight glazing.

Exclusive online content These animations (Animation 1) demonstrate a condition in the transition panels discovered during the full-scale mockup. On June 21, during the hours of 10:30 to 11:50, direct daylight enters the third-floor galleries. The blue surface seen in Animation 2 is the area covered by the custom frit pattern applied to correct the problem. (Please note: The files are large and will take a few minutes to download. They also require QuickTime 5.0.)

Bold in its 7-foot-tall form, the daylighting system is completely passive, featuring no moving parts, explains Davies. Instead, it is comprised of three elements: The ôsoffitto,ö a tubular unit constructed of glass-fiber-reinforced gypsum on a 4-foot-square module, diffuses and directs light from the skylight (shown in yellow). The skylight, cut at an angle with the lowest point facing north, features low-iron glass with a low-E coating and a laminated interlayer (shown in red). This glass arrangement facilitates a high CRI, prevents UV rays from entering the gallery, and helps maintain thermal criteria. The white aluminum ôvelas,ö oriented due north 26 degrees off the buildingÆs axis, are the final piece (shown in blue). A combination of the northern orientation and reflected sunlight, bounced into the galleries off the white surface of the vela in front, helps capture the appropriate amount of light from AtlantaÆs sunny climate. There are 1,000 of the skylights in total: 800 on the Weiland Pavilion and 200 on the Anne Cox Chambers Wing.

While the daylighting system plays an obvious role in the architecture, the electric lighting concept was also important, especially on the lower floors where natural illumination was not as available. Inside, track lighting (an iGuzzini fixture designed by Piano) supplements the sunÆs rays. The track is on two circuits: one controlled relative to the amount of daylight, and the other independently to meet the requirements of the artwork. Generally, however, the ambient illumination in the third-floor galleries is generated by the sun. ôIt is a certain quality of light that is not often used in American museums, and a good demonstration of how natural light can be applied,: says Davies. "It will encourage discussion, I think."

project High Museum of ArtÆs Wieland Pavilion and Anne Cox Chambers Wing, Atlanta
architect Renzo Piano Building Workshop, Genoa, Italy, in collaboration with Lord, Aeck, Sargent Architecture, Atlanta
lighting designer Arup Lighting, London
engineer Arup, London and New York
photographers Jonathan Hillyer (exterior and interior gallery shots); Floto+Warner, New York (close-up of skylight)
animations Courtesy of Arup Lighting