Daylight penetration into a deep interior space can be achieved by using a light tube strategy. This research investigates how effective a room's ceiling cavity can be as a daylight transporting system. The design, therefore, tries to answer the question "What is the optimal geometry for a ceiling cavity and inlet aperture to bring deeper daylight penetration and achieve a higher illumination level, measured at the back of a room, than that achieved by a typical high window opening?" Corporate affiliate 3M assisted this project by providing a prismatic and highly specular surface to cover the underlying geometry of the ceiling cavity. A 16' deep room section with a high window opening on one side was constructed as a test cell. Inside, sensors were set up to allow light measurement at task level along the depth of the room. Light rays were deflected by the geometry of the ceiling cavity, through a number of internal reflections on the highly reflective film surface, to a diffuser at the back. The three most promising geometric designs from scaled model tests were selected, installed and tested for efficiency in the full-scale test cell. / Master of Science