A Treatise on Painting
by Leonardo da Vinci, translated by John Francis Rigaud
Of those Painters who draw at Home from one Light, and afterwards adapt their Studies to another Situation in the Country, and a different Light
4009426A Treatise on Painting — Of those Painters who draw at Home from one Light, and afterwards adapt their Studies to another Situation in the Country, and a different LightJohn Francis RigaudLeonardo da Vinci

Chap. CLXXXV.Of those Painters who draw at Home from one Light, and afterwards adapt their Studies to another Situation in the Country, and a different Light.

It is a great error in some painters who draw a figure from Nature at home, by any particular light, and afterwards make use of that drawing in a picture representing an open country, which receives the general light of the sky, where the surrounding air gives light on all sides. This painter would put dark shadows, where Nature would either produce none, or, if any, so very faint as to be almost imperceptible; and he would throw reflected lights where it is impossible there should be any.