Two of the windowless north galleries of the second floor receive direct sunlight that passes through the high southwest windows of the atrium (see yellow areas in Figure 4- right). Illuminance levels measured over the painting in one of the two galleries on January 19, 2003 (Figure 15) reached an extremely high value of 11,500 lux, which is about 57 times higher than the recommended IES standards for museums. The total illuminance-hour per year over these display areas over exceeds the total exposure limits for moderately light susceptible displayed materials. The fish-eye photo (Figure 16) shows that the painting receives direct sun for one and a half hours in the early afternoon from November to January. The high illuminance levels over the display areas are due to the high visible transmittance of the atrium’s glass (Tvis=59%). The glass of the atrium does not have any shading device to intercept the incoming direct sun to the adjacent galleries. To protect paintings from over exposure to light, curators have been rotating oil paintings frequently (see dates on Figures 15 and 16).

Figure 16: Fish eye photo taken from painting’s viewpoint with sun path diagram, at gallery adjacent to atrium (March 5, 2004).

Another problem observed in these galleries is the glare that visitors experience while moving through the gallery and to the atrium. Figure 17 illustrates how a visitor has to protect her eyes from direct sun while trying to see the painting and read the sign next to it. This visitor is receiving about 7,770 lux over her eyes when not covered. The extremely high variations of light levels within the field of view of the visitors to these galleries makes them uncomfortable to adjust their eyes to the low light levels over the paintings and to the bright atrium’s glass areas that are within her field of view.

Conclusions

The most noticeable problem, in the galleries of two of the museums presented in this paper, has been the sunlight penetration over the displayed museum objects. This fact is harming valuable art collections, and also creating visually uncomfortable environments for visitors. Sunlight penetration occurs mainly in galleries with side lighting windows that face the sun — east, south, and west-; orientations that are the most difficult to control. Even though the time of over exposure is relatively limited, the illuminance levels reached at these times are extremely high, 10 to 57 times the maximum recommended IES standards for light susceptible objects. Dark tinted glass, screens, or small overhangs are not enough measures to block the entrance of direct sun over the exhibit areas at the Modern Museum (west-facing galleries) and at the Amon Carter Museum (east-facing galleries).

To control the light levels in these galleries more aggressive changes should be done, like modifying the fagade by adding horizontal or vertical shading devices, external louvers, trellises, or trees to filter sunlight. All these modifications could change the image of the building, which may not be acceptable by designers. There are other less intrusive solutions that include the use of miniaturized sunscreens, interior louvers or baffles; or computer controlled dynamic window systems (Reference 6), where direct sunlight over sidelight windows can be intercepted and filtered reducing interior light levels as low as 25 lux or under.

On the other hand the third museum, the Kimbell Art, presents a well thought and carefully designed toplighting system that can introduce adequate light levels throughout the year to accommodate the lighting requirements of exhibits, and at the same time provide a connection to the exterior environment by rendering the galleries with natural light. This museum is an excellent example that it is possible to successfully illuminate museum galleries with daylighting.

If we already know that sidelight windows in museum galleries create many problems to the display of light susceptible artifacts, why are we still including them as a source of illumination in museum galleries? Is it due to the lack of knowledge about solar geometry? Or it is just that architects underestimate the effects of sunlighting in museums? The answers to these questions may not be clear and simple, meanwhile we might be finding museum galleries with sidelight windows with strong sunlight over display areas, such as in two of the three museums presented in this paper (see summary in Table 1). In the meantime, curators and facility managers at these museums have to create means to protect their valuable art collection (i. e. rotating display objects, use boards to cover them on a daily basis, display least light susceptible objects, cover completely the windows with boards or black cloths, among other solutions) (Reference 7). The main goal of this paper was to make us reflect on the way that museums are still being designed, and on how could we make them better to preserve and display artifacts that are important part of human history.