I think a lot of people do not think enough about proper lighting when they paint. I am currently setting up my paint desk so thought I would take some photos of my thoughts around this.
Single light: Roof lamp over my right shoulder.
For me being right handed it is bad, as it creates a shadow where i want to put the brush.
If I were left handed however, it would be good as the shadow does not land where I am painting.
Single light, a desk lamp to my left in an otherwise dark room (turned the roof light off)
For me being right handed this is good as the shadow falls on the correct side but a model probably needs better light in the room itself to show all the colors correctly.
If I were left handed this would be a horrible shadow to work with.
Two lights: the roof light (farther away) plus the desk lamp on my left (stronger/closer).
Right handed, good. Although there is a shadow on both sides at least the undesired one is weaker.
Left handed not good, as the stronger shadowshadow in on the painting side.
In short, make sure the strongest light comes from the side opposite your paint hand. This will combat shadow on the surface you are painting.