just isn't as popular in planted aquaria, because most of the time the tank sizes don't get big enough to merit the expense of MH
From my understanding, MH
is slightly less efficient than fluorescent lighting, in terms of lumen output per watt consumed by the bulb.
You could follow the basic guideline of WPG
, but feel free to go over it just a little. For example, power compact users can grow glosso with 2.5wpg...but with MH
I'd go for a full 3wpg.