Challenges in the simulation of the daylight distribution in late antique Hagia Sophia

The deliberate utilisation of daylight has been discussed as an outstanding element of the design of Hagia Sophia in Istanbul starting with late antique sources, and continued through the centuries up to our day. Computational simulation allows to reconstruct this illumination. This - for the first time - offers a means to relate historical descriptions and modern hypotheses with daylight as a physical phenomenon, but requires a sound methodological basis to provide valid results. Bidirectional photon-mapping is demonstrated to predict the propagation of light in the architectural space, characterised by complexity with regard to its geometry as well as the optical properties of its boundaries. The latter must be reconstructed in their original condition, eliminating modifications of the original building composition as well as deterioration of the material and finishes of building elements. The description of the latter’s irregular properties suggests data-driven modelling based on gonio-photometric measurements. Either realistic or representative description of sky conditions based on climate data or high dynamic range imaging techniques is presented and critically discussed, since it provides descriptions of the contemporary conditions. Finally, the transfer of simulation results from the physical, photometric to the perceptual domain is necessary for any interpretation in the historical sciences, and to relate the quantitative outcomes to written accounts. The authors present methods and results from the exemplary application to the case of Hagia Sophia from their ongoing research. A research agenda is proposed to close the gap between archaeological evidence, advancements in the reconstruction and computational simulation of lighting, and its potential contribution to the historical sciences in arts and building.