Holy cr@p, Ray! :shocking: :)
As another data point for the OP, I have twelve 4-ft two-bulb T-8 shop-light-style fixtures with 5000K bulbs in my 24'x24' garage. The ceiling is galvanized corrugated metal, as are the walls 3.5 feet up (but most of it is hidden by shelves, cabinets, equipment...