Lighting levels with High Efficiency Fluorescent Tubes
The design suggestion for using High Efficiency Fluorecent Tubes was to place only 2 tubes on a 3 tube fixture, and to disconnect some fixtures. It is common in shopping centres and government buildings around here.
It is sold as a power saving measure. Perhaps part of the reason they get away with it is that new tubes are always brighter than old tubes, so you don't get a fair comparison when you replace 3 old tubes with 2 new tubes: the new tubes are bright by design, but also bright by newness.
In any case, I would not place 2 bright tubes in a fixture built for 3 old-design tubes: given the choice, I would make my school, government and shopping buildings brighter, because I focus better in brighter light.