A Treatise on Painting/Chapter 191
Chap. CXCI.—Whether the Light should be admitted in Front or sideways; and which is most pleasing and graceful.
The light admitted in front of heads situated opposite to side walls that are dark, will cause them to have great relievo, particularly if the light be placed high; and the reason is, that the most prominent parts of those faces are illumined by the general light striking them in front, which light produces very faint shadows on the part where it strikes; but as it turns towards the sides, it begins to participate of the dark shadows of the room, which grow darker in proportion as it sinks into them. Besides, when the light comes from on high, it does not strike on every part of the face alike, but one part produces great shadows upon another; as the eyebrows, which deprive the whole sockets of the eyes of light. The nose keeps it off from great part of the mouth, and the chin from the neck, and such other parts. This, by concentrating the light upon the most projecting parts, produces a very great relief.