In the present example, an appropriately large room was to be designed specially for a sculpture by Walter de Maria, which because of its size could previously only be exhibited by distributing it over different museums. The design by Peter Zumthor included a support-free exhibition room measuring about 70 m x 70 m with natural lighting only (no artificial light installation). The daylight enters the room from above via the large ceiling grid. The grid was dimensioned by the architect with the aim of only allowing the sun to briefly shine through at 9 o’clock in the morning and 3 o’clock in the afternoon on midsummer’s day. However, the astronomical studies revealed that this ‘Pyramid effect’ with the sun shining on one single day in the year would only be achievable during the periods around the equinox. At the time of the longest and shortest days of the year, the daily change in the sun path is smaller than the apparent diameter of the sun, meaning that the sun is almost in the same location at the same times for several days. (sun penetration, right-hand diagram) As far as the design is concerned, this means that the grid allows sun penetration for a brief time during the day for 1-2 weeks around the 21st June.			Plans	Roof grid
			Sun penetration