you want to match at the very least, one watt per gallon of water. the other thing to consider is the Kelvin rating. most people use anything from 5,000K to 10,000K. i use two 40 watt bulbs at 6,500K to light my 55 gallon planted tank. that gives me 80 watts of light for 55 gallons of water or just under 1.5 watts per gallon. i stick to low light plants and i have good results without resorting to a lot of fertilizers or a co2 system.
honestly, if you are trying to keep plants, too low a wattage could end up leaving you with algae problems. the different types of bulbs (like T5, T8, T12) give you different bulkiness and power consumption (for your electric bill, not so much for output). my fixture holds 2 T12 bulbs. the downside is its bulky. the tubes are big and it stands pretty high which means i have to redo my canopy because the sides dont fit right now. its up to you
honestly, if you are trying to keep plants, too low a wattage could end up leaving you with algae problems. the different types of bulbs (like T5, T8, T12) give you different bulkiness and power consumption (for your electric bill, not so much for output). my fixture holds 2 T12 bulbs. the downside is its bulky. the tubes are big and it stands pretty high which means i have to redo my canopy because the sides dont fit right now. its up to you
