Le Thoronet is one of three wonderful Cistercian abbeys in Provence, built around 1170. In the mid-twelfth century this part of southern France was not a major tourist destination. The monks who built Le Thoronet were avoiding the political intrigues and feudal power struggles of the cities by locating in a remote area, and they weren’t necessarily welcoming company. And they were building for eternity, too, so the walls are thick, sometimes over three feet thick. As with a lot of ancient masonry construction, this has a salutary effect on the way daylight works in the interior. Why?
In contrast to today’s vogue for all-glass buildings, how is it that massive masonry construction can result in wonderful daylighting? This has a lot to do with contrast control, which is related to the deep apertures created through the thick walls.
Because sunlight is such a powerful light source, a major challenge with daylighting is to moderate the contrast between very bright exterior views and the relatively much darker interior surfaces. In particular, the interior face of the wall containing the window often tends to be the darkest surface in the entire space, since it may receive no direct daylight at all. This can result in very harsh contrast at the apertures. But, when the aperture has depth, the sides of the opening provide extensive surfaces with a brightness that is intermediate between exterior and interior, graduating the contrast.
Without this kind of buffer, the contrast is often more than the eye can comfortably accommodate. If splay or architectural ornamentation is present in that zone, the contrast gradient is even more improved; the ornamentation itself is beautifully rendered by the raking light and brightness gradient from exterior to interior.
In addition, those surfaces, especially the sill, diffusely reflect daylight into the interior – for example, illuminating the ceiling even though most of the original daylight source is heading for the floor.
These are daylighting principles we would do well to emulate in our designs today. We’re rarely going to have walls three feet thick to work with, but we can accomplish similar effects by, for example, positioning our apertures against flanking walls or piers. In this house by Tadao Ando, the room surfaces perpendicular to the apertures have a brightness intermediate between the view outside and the darker interior surfaces. In addition, they diffuse daylight back onto the inside surface containing the aperture, which further softens contrasts.
The deep aperture approach lies in stark contrast to just treating daylight apertures like simple holes in the wall. Besides improving contrasts, the deep aperture uses daylight as a powerful expression of the extension of space.