What did Leonardo believe about light in art?

Answer 1

The 2nd quote from the person above me is about lighting a still life. You should always paint in north light because the shadows will change slower sense The sun hangs out in that part of the sky longest.
Leonardo like alot of classical painters believed that 'light comes from heaven.' as Hale put it. The up facing planes would be light, the down facing ones would be darker.
Almost all classical work is lit from the top left slightly behind the viewer.
All his work shows the use of reflected light and core shadows.
His Color work was done using warm and cool contrasts based on the light. A natural light casts a cool light, a lamp or artificial light produces a more warm light. These will effect how the artist paints the image.

Answer 2

He kinda discovered soft lighting. I don't know what he 'believed' about it but he sure was the first master of soft focus.