Spanning the area between painting and sculpture, Knoebel's main body of work is in the Constructivist tradition. 'Projection X', his only videotape, was one of a number of works made in 1970-71 that were based on outdoor projections. During a nocturnal drive through the sleeping city of Darmstadt, a large, luminous X is projected from the vehicle onto the walls of buildings. Due to the uninterrupted 40 minutes recording time, and the video-specific streaking, or comet, effect that occurs in poor light conditions, the tape is distinctive for being one of the few Schum productions specifically geared towards the video medium. As such, it may be seen as exemplifying Schum's transition from the 'TV exhibitions' to the more art-world oriented 'Video Gallery'.