Throughout the medieval period, Christian churches were designed in such a way that natural light was deployed to underscore a variety of theological statements. The solutions usually found in Latin and Byzantine churches have been analysed in recent decades. However, the cultures that developed at the crossroads of the Latin, Greek, and Slavic cultural spheres, particularly in regions of the Balkan Peninsula and the Carpathian Mountains, advanced their own formulas for how to use natural light in ecclesiastical buildings. These solutions depended on know-how inherited from Antiquity, and were further shaped by local climatic, economic, and theological parameters. The present workshop invites papers on the economy of natural light in medieval churches constructed across Eastern Europe, from the Balkans to the Baltic Sea, and throughout the medieval period. Whether adopted or inspired from the more established traditions on the margins of the Mediterranean, local customs are examined in order to understand how natural light phenomena unfolded in ecclesiastical spaces, and how they related to the design, architecture, decorations, liturgical objects, or rituals performed inside the buildings. The multilayered analyses of light Inszenierung examined in this workshop cast light on the structuring of sacred spaces in the Byzantine-Slavic cultural spheres. Moreover, the expertise behind the deployment of these natural light effects reveals patterns of knowledge transfer and cultural interaction between Byzantium, the West, and the Slavic world that extended in regions of Eastern Europe during the Middle Ages.