Depends on many factors, height of ceiling, whether computers are in the rooms or not, what the depth of the void is, whether books are read or not, fire rating of ceiling, what lux levels are required, can be anything from 300-500 lux, you need to consider all options, when I work in offices I always get a lighting manufacturer to design the scheme, ring the reps from Thorlux, Dextra or Thorn for example, they calculate everthing concerning the actual working enviroment and client needs and the responsibility will be off your shoulders, in a commercial enviroment guessing is out of the question, I do 95% of my work in this sector and have seen everything problem wise, get a lighting company to take the pressure of design off you, or get some Indemnity Insurance, and take a gamble, I wouldn't though
