I'm not sure my answer will be of any value, my shop is a 12x24 shed out back... initially I had 6 4' fluorescent shop lights hung around, one directly over the lathe, one over each of the work benches and a couple for general lighting... I do have some dark corners that I need to add a couple of lights to...I say I had 6 initially, but a few months back the one over the lathe got knocked down when a bowl exploded and a projectile piece took out the fixture... ruined a perfectly good pair of shorts and left me ducking for cover.... I'm still even after several months picking up pieces of glass here and there.... I moved one of the other lights back over the lathe, hence the dark corners.... I also have a articulating desk light afixed to the wall that I can direct to my work piece and since my lathe sits in front of one side of the double doors to my shop, I can open both doors and have lots of natural light.
How much light is a subjective subject, that relates to your own personal preferences.