Perspectives on light scattering by window glass in Hagia Sophia

Daylight in Hagia Sophia and its effects have been prominently described by historical and modern authors, and inspired later building designs over centuries, motivating a closer and systematic look at the windows of the late-antique church. In particular the window glass, that has not been preserved but formed the interface between incident light and daytime illumination of the interior, shall be addressed. For a plausible type of window glass, the impact of production techniques on light scattering properties shall be summarised. Taking into account the configuration of the windows in Hagia Sophia, the perception of window glass as a) a filter for the illumination of the interior, b) directly visible surfaces lighting up under direct sunlight, c) the possible veiling effect and d) reflection of these surfaces on specular, opaque surfaces, and finally e) transparency and the question whether the windows provided a view to the exterior shall be discussed. Seasonal and diurnal variation of these effects shall be illustrated for selected time-steps that are related to the liturgical use of the building in the sixth century. The authors hope to provide a useful terminology for historical research addressing daylight in buildings beyond the chosen case of Hagia Sophia.