Transmissive properties of Medieval and Renaissance stained glass in European churches

Abstract

Medieval stained glass is often described by how its clarity contributes to the lightness or darkness of a sacred interior. Using high dynamic range (HDR) imagery (a low-budget, time-efficient means of photographic data collection) to estimate luminances (or per-pixel brightnesses), the relative transmissivities of adjacent panels of glass are obtained for the first time in a variety of medieval churches in western Europe. In order to carry out a comparison between different interiors, red glass was assumed to have a fixed average transmissivity, based on data that suggest that the glazing transmission of red panes is relatively constant. This red standard was then applied over a large database of images collected from different churches to provide a quantitative index of stained glass light transmission. The results indicate that the use of brighter colours during the 12th century admitted more light compared to 13th-century glass. Furthermore, the more translucent glasses of the 15th and 16th centuries appear to have increased light transmission into the interior by as much as an order of magnitude. The resulting change in indoor illumination significantly altered the human visual perception of the sacred interior as glazing preferences evolved over the course of the late Middle Ages.