Hi there ya all. Just a quickie thought, appears that your calcs takes into consideration the burner (bulb or tube) only, there are losses with the control gear as well, abt 5%. (that is the heat you feel coming off the box) I'm talking about a HPS setup, though same is true of fluros too, though to a lesser extent. Generally, there are higher losses in older control gear (more total watts) and less light from old burners. (things don't grow as well or happen as fast.) Cheers . .