Hagia Sophia’s sixth century daylighting

Abstract

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 analyse this illumination, and to understand the day-lighting concepts inherent in Hagia Sophia’s outstanding architecture, employing computational simulation based on the reconstruction of the building’s geometry at the time of its second dedication. Accounted for are 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 optically complex gold mosaics. Daylight simulation under a synthetic sky with varying solar geometries and cloud coverage reveals differences between the historic and present states, e.g. higher diffuse illumination originating from the windows of the aisles and galleries; effects of light scattering by 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 affect the 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 particularly impressive lighting on the Christmas morning.