This Working Group chapter project was an exploration of the optical sources used by Leonardo da Vinci in his research on shadows. As most sources of the Renaissance were available in Arabic and Latin, the focus was mainly on translation and knowledge transmission.
Leonardo’s research into light and shade is well known in architecture and art history, because shadow is directly involved in the rendering of volume and depth. Leonardo’s studies paved the way to the tracts on shadows appended to many perspective treatises from the sixteenth century on. Leonardo is also well known to historians of optics, because he provided one of the very first studies of the penumbra—a concept further investigated by Maurolico (Photismi de lumine et umbra, 1521, theor. 18) and Kepler (Ad Vitellionem Paralipomena, 1604, cap. VI, 7), who first coined the term penumbra. The penumbra denotes the partial shadow, that is, the mix of light and shade that occurs when the light source is greater than the opaque body. Leonardo, who used the word ombra semplice for the full shadow and ombra composta for the partial shadow or penumbra, has been regarded as reaching the first milestone in the discovery of the concept of the penumbra. This was well before Maurolico (1521) and Kepler (1604). However, there is evidence that the geometrical analysis of the penumbra was already in place in Ibn al-Haytham’s Epistle on the Properties of Shadows and that Leonardo used external sources on this subject. This chapter reviewed the medieval optical sources he could have used to compose his notes.
A careful study of Leonardo’s notes reveals that they were probably translated from a scholastic disputation on optics, akin to the works of the late fourteenth-century Parisian school. Information is provided for future identification of this treatise.