The main entry lobby to the museum is used as a gallery for the display of oil paintings and metal sculptures. In 1996, Philip Johnson made changes to the museum’s east fagade by replacing the glass to a dark tinted one with visible transmittance (Tvis) of less than 5% and UV protection. Even with those modifications and the arched portico, direct sunlight strikes the lobby every morning throughout the year except few days around summer solstice. The fish-eye photo from Figure 8 indicates that the painting receives direct sun year-round for about 55% of the morning hours. The horizontal ceiling of the portico protects the paintings from the sun for about an hour everyday of the year. Figure 9 shows the amount of sunlight penetrating this gallery on March 5 at 9:00 AM. Illuminance levels measured over the paintings at this time reached values of 2,400 lux, which is about 12 times higher than the recommended IES standards for moderately light susceptible display materials. Every night each of the oil paintings of this gallery are covered with boards to protect them from the morning sun and UV radiation. Every morning, the boards are removed from the painting few minutes before the museum open its doors for visitors (10:00 AM).

South-facing gallery (2nd floor):

This gallery is the only one on the second floor that receives natural light directly from a side light window. The gallery is located right over the South entrance to the museum.

The gallery displays mainly oil paintings and metal sculptures (Figure 10). The 210-ft2- window area (19.5 m2) has a five-feet (1.5 m) external horizontal overhang, and the visible transmittance (Tvis) of the glass is 12%. The window wall ratio (wwr) of the gallery is 58%, and the window floor ratio (wfr) is 28%.

Direct sunlight inundates the gallery all day throughout the year. Fish eye views taken from the painting’s viewpoint show that it receives direct sunlight between 2:00 and 4:00 PM from November to January (Figures 11 and 12). Illuminance measurements taken over the painting under direct sun reached up to 2,200 lux, which is 11 times higher than the IES recommended standards for oil paintings. The total illuminance-hours during these two hours of sunlight over the painting is around 404,800 lux-hours, when added the illuminance-hours over the painting during the rest of daylight hours 700,000 lux-hours, the total over exceeds the maximum annual exposure to light recommended by IES for oil paintings. Figure 12 also shows that the horizontal overhang blocks sunlight few hours around wintertime, but does not shade enough the window to protect the painting. Paintings in this gallery are exposed to daylight at all times without any device that could help to reduce the illuminance levels over light susceptible artwork.

Figures 13 and 14 show the illuminance levels simulated with the Desktop RADIANCE lighting program in the south gallery on November 28, at 3:40 PM. Simulated illuminance levels were calibrated with the measured illuminance levels during site visits. Lighting simulations were done at different times during the day to evaluate the sunlight patterns in the gallery. Results from these simulations showed that the display areas over the walls

receive direct sun in the morning (west wall) and afternoon (east wall) for about two hours around winter solstice.

Figure 14: Radiance model of Amon Carter Museum’s south gallery on November 28 at 3:40 PM; false color image with illuminance levels (bottom).