how long should i leave my light on

[I'mHooked]

I leave my lights on for 10 hours a day, with 4 watts per gallon over my tank. I use sunpaq bulbs by CurrentUSA. Longer hours give your plants a better chance to maximize photosynthesis, but like others mentioned above, if your nutrients are out-of-whack to go along with the higher levels of photosynthesis then you're going to have algae problems. I'm going to up my time to 11 hrs here in a couple weeks. It really just depends on how good you are at dosing fertilizers.