Mike
having no natural light does explain your situation better.
As for the wiring, I think that would be quite normal, after all, your domestic lighting is just the same, its just that usually the wire run is hidden.
The numbers of course don't explain everything, it depends also on the wattage.( brightness) of the bulbs
Placement is important as well.
Bottom line is, if there is not enough light either replace them with brighter bulbs( if possible) and/or increase the number of fitments
Edit: Check that your fitments can take a more powerful bulb or tube though