Hagia Sophia's sixth century daylighting

Since its construction in the sixth century, Hagia Sophia has been praised for its lighting. While some aspects of its illumination can be studied in the present building, the totality of its primal appearance has been lost due to supporting measures, additions and later changes. An attempt is made to analyze this illumination, and to understand the daylighting concepts inherent in Hagia Sophia’s outstanding architecture, employing computational simulation. It is based on the reconstruction of the building’s geometry at the time of its second dedication, and the original distribution and properties of the surfaces enclosing the architectural space, including the detailed marble decoration, the original gilding of sculptural elements, and the complex gold mosaics. The results of daylight simulations under a synthetic sky with varying solar geometries and cloud coverage show differences between the historic and present states, such as an absolute higher diffuse illumination originating from the windows of the aisles and galleries, effects from scattering window glass, and the unimpaired appearance of marble, gold mosaics, and gilded surfaces. The results allow to ascertain how the contributions of different groups of windows result in a dynamic interplay of direct sunlight, diffuse illumination, and the specular reflections on mosaics and marble, changing with the exterior sky conditions. The results further show that the orientation of the building produces a particularly impressive lighting at the Christmas morning.