Leading Light (1975)

"John Smith's Leading Light evolves a sense of screen depth and surface through the simple agency of light. The film is shot in a room over a period of a day and records the changes in light through the single window. The image is controlled through manipulation of aperture, of shutter release, of lens, but the effect is more casual than determined and the spectator is aware primarily of the determining nature of following sunlight."
Deke Dusinberre 'Perspectives on British Avant-Garde Film' catalogue 1977