The watts per gallon required for low, medium and high lighting depends on the light type being used too. AH Supply kits are, in my opinion, very good both as to the bulbs and to the reflectors, so less watts per gallon are required with them than with T8 fluorescent bulbs with white painted flat reflectors. And, the watts per gallon also depend on how high above the tank the light fixture is. The higher the fixture, the more light is lost due to spillover. (If the reflector is reasonably good, and the bulb is down in the reflector far enough, the loss of light by the square of the distance is not the most significant loss.) So, in my opinion again, it isn't really possible to say how many watts per gallon equal high, medium or low light without also saying a lot more about what lights and how they are mounted with what reflectors. I think that's why the watts per gallon "rule" is nothing more than a crude ballpark estimate of the amount of light needed.