Leonardo Da Vinci made a scientific study of light and shadow in nature. He concluded that there were three elements to objects - 3 dimensions - each defined by light & shadow. His note books 1452 - 1519 contain a study of PENUMBRAE the zone of partial shadow where an object is only partially obscuring a light source.
I also plan to look at Caravaggio - the techniques of Tenebrism & Chiaroscuro (?), Albrecht Durer, Rembrandt... and the scene in Peter Pan where he looses his shadow and Wendy sews it back on.