IMO, low/med/high would have to take into consideration the intensity and wattage. It would have to also take into consideration where the corals would be placed in the tank.
If you were going to place the corals near the top of the tank, then that would probably be on the high side of medium lighting.
But other than the top, I think DvSkin has it right, medium-low lighting. You couldn't allow something that required medium/moderate lighting to thrive on the bottom as well as it would do if you had more intense lighting.
The root of the problem with watts per gallon and any thumbrule for that matter:
Assuming you have two tanks; All are 24" high (water depth) 18" deep (front to back) and then one is 1 ft wide, the second is 2ft wide.
You take the 1 ft wide tank and put 12" bulbs (these are just some fictituous bulb...) that are 50 watts each. You have 2 over this tank.
The next tank has 2 ft long bulbs (since it's a 2ft long tank) and they are 100 watts each.
The first tank now has 100 watts and the second has 200 watts.
You practically have no difference in the lighting of these tanks... Now if you took the longer bulbs, and put them over the first tank, you would now have 200 watts over the 1 ft long tank... Again, you practically have no difference in lighting, since lighting per square inch, square ft, etc... has not really changed. The intensity has not increaded/decreased, simply put longer lights over it. You have effectively kept the same amount of light but doubled your watts per gallon.
There are of course studies that do this sort of test, and yes, you would have a little more light, but not near what the watts per gallon would make you think..
You could prob get more complicated, and compare it to something on the order of the microscopic cross section of absorbtion, and say that there is a given amount of energy in each area given off by the bulbs. What are the chances of that energy interacting with the specimen or interacting with water and never reaching the coral on an atomic/molecular level; if you doubled the intensity (or energy across that area) you have now practically doubled the chance for absorbtion, effectively increasing the microscopic cross section of absorbtion due to having twice the energy to make it through the molecules of water and now available for interaction with the coral.
And ofcourse, the deeper the tank, the more watts you will need per given area to get as deep, erego, mh for deep tanks, since they are the only one intense enough to provide the high watts in a compact area.
Ok, that may be too far off track. Oh well... Anyway
I agree if DvSkin and Michael
The key to high lighting is intensity.
Gator
