The article examines the change in luminosity in Gothic stained-glass windows, based on examples from France. This change began around the middle of the 13th century, when coloured panels were increasingly set into grisaille glass. The joint use of clear glass with intensely coloured glass on the one hand allowed more light to enter the interior of the church, and on the other led to different design solutions for combining coloured images with the grisaille. This brought about the evolution of (...) the band window in which one or more horizontal series of coloured figurative panels crossed over the narrow mullions against a ground of grisaille. In order to explain the development of composite windows, material arguments (economic constraints, technological progress) as well as non-material arguments (new aesthetic) have been advanced and are critically considered. The focus of the article is on the effect of the media synthesis between stained glass and architecture with regard to the visual projection of the images. (shrink)