Bob,
If I remember my physics right, the inverse square law applies to a point
source light, that is a theoretical point source. The classic illustration
in your high school physics book used a candle and a grid that was
illuminated by the candle. Diffused light, tubes, lights with reflecting
backs, collimated light, all do not obey the inverse square law and are all
closer to some lesser fall off. For a fluorescent light bank to behave this
way, you would need to get far enough away for it to act like a point
source. For a 4 ft square bank, I'd say something like 5o + feet would start
to behave in inverse square manner.
Dick Sullivan
Bostick & Sullivan
1541 Center Dr.
Santa Fe, New Mexico
87505