I think the reason why we think watts per gallon is that it makes picking the right lights somewaht an easier chore. Most of the inhabitants excluding fish require light intensity and not so much watts per gallon though.
When using flourescent bulbs, the intensity is nowhere the same as MH
because the MH
gives off a better UV
rating and lumen, CRI index which is most important to anemones, corals, and photosynthetic animals. This is why you can have 2 - 175 MH
and have more usable light than 4 VHO
's. The direct intensity of MH
has been proven to out perform flourescents many times over, and it will continue to. There is no getting around that. The CRI index of MH
is 94 - 96 which is as close to sunlight or correct light you can get right now. Flourescents are 10 below at 84 brand new and then in the 60's shortly thereafter. This is why watts per gallon is somewhat neccessary with Flour's...
For instance lets say 3 watts per gallon is ok:
4 - 40 watt tubes = 160 watts = roughly 3 watts per gallon on a 55 gal
tank. but put that on a 75 gal
tank and you have 2 watts per gal
. go to an 80, and you have less than 2 watts per gal
...nowhere near enough light to generate enough intensity.
4 - 110 watt VHO
's = 440 watts = 8 watts per gallon on a 55. go to 75 gal
tank and you have 5.8 watts per gal
. go to an 80 gal
tank, and you then have 5.5 watts per gallon and though this will give you good results, there is still a lot of lost intensity.
Now, go with
2 - 175 MH
accented with 2 NO 40 watt actinics and you have 430 watts wich gives you 7.8 watts per gallon on a 55 and 5.7 watts per gallon on a 75 gal
tank and 5.3 watts per gal
on an 80 gal
tank. This will be an excellent option on any tank and you can up the intesity and wattage by getting higher rated bulbs. e.g 250, 400 watt etc... This will up the watt per gallon and also up the intensity to a 94 to 96 CRI.
Watts per gallon is a matter of personal preference really and it is still debated if it holds any weight. I use it because I use flourescent bulbs. When I go to MH
it won't matter much. I hope this is useful to anyone who is interested in the theory...
This is all on me and not the opinion of the masses...