I have built a large shop with ten-foot ceilings. Since I had about thirty fixtures (dual, 40 watt shop lights) I used them. (Hindsight would suggest that running continuous dual eight-footers would have been a better choice.) They are hanging about seven inches from the ceiling. The drywall walls and ceiling are painted white. (Actually, white base with 5/96 of an ounce of magenta per five gallons just to make it a bit warmer than pure white. If I had it to do over I would go with 5/48 of an ounce of magenta.)
I have a smooth, bare, gray concrete floor which will have a light almond epoxy applied soon.
I installed 27 fixtures in an area just under 1400 sq. ft. When I turn them on I find it is almost too bright, and will be even more so when the floor is painted.
The numbers are: 27 x 2 = 54 four-foot, 40-watt fluorescent bulbs. 1387 / 54 = ~one 40 watt bulb per 25 sq. ft. or 1.6 watts per sq. ft.
I would now say that 1.5 watts per sq. ft. is more than enough light for my type of building. Probably 1 watt per sq. ft. would be adequate. YMMV.
-Doug in Utah