For a more direct experience of being in the park, glazed walls make up 20 percent of the building's perimeter. Strategically located, one glass-enclosed gallery overlooks the outdoor sculpture garden. Guided by an astronomical clock working with rooftop photo sensors, two layers of vertical shades control light levels within this and two other windowed galleries. A light-reducing shade allows views out to the park when down. A more opaque, diffusing shade allows little light transmission and is typically set 7 feet above the floor, descending completely only when the sun is very low. The shades are operated by the same manufacturer's control system, which has been modified to meet the specifications of the museum. “The intent was not to have the shades continuously open and close, as that would be very distracting,” says Christopher Rush, senior lighting consultant at Arup, the firm charged with the project's overall illumination. “The general idea is to keep both sets of shades open as much as possible.”

To balance daylight with conservation needs, the client and lighting designers agreed on a cumulative-exposure approach whereby the curators track average light levels over the course of the year, rather than set maximum exposure levels for any specific time. Blackout roller shades directly beneath the skylights are deployed when the museum is closed, decreasing average daylight quantities.

Electric lighting is used when sunlight levels are low—in the winter or when the museum is open at night. Fluorescent tubes tucked above the coffers provide cool ambient light, while halogen spotlights on a track built into the framework around the light spreader animate artworks. The effect can be brilliantly seen on St. Louis native Tom Friedman's “Untitled” (Seascape), 2012, a trompe l'oeil paper construction, with creases and wrinkles that evoke waves. “This piece needs light from above to bring out its full complexity,” says curator Simon Kelly. “General diffuse light doesn't show this off optimally.”

Properly displaying the artwork remained a constant consideration. “The challenge was making all of the technology invisible,” explains McFarland. “When you look up to the coffers, you have no idea how much stuff is going on there!”