A Treatise on Painting/Chapter 186
Chap. CLXXXVI.—How high the Light should be in drawing from Nature.
To paint well from Nature, your window should be to the North, that the lights may not vary. If it be to the South, you must have paper blinds, that the sun, in going round, may not alter the shadows. The situation of the light should be such as to produce upon the ground a shadow from your model as long as that is high.