““Yet another strategy for encoding in Renaissance works involved environmental “special effects.” Messages were ingeniously inserted so that they could be viewed only when one was in situ, in the very spot where the artist intended for the viewer to receive his true intent. Often this would be determined by how light coming from an actual window at the site would stream into the painting, thus literally and figuratively illuminating the piece. Leonardo did this with the light in his Last Supper fresco,””
