Drew 43920

They say that a low-light tank should have 1.5 watts per gallon. OK.
But for how many hours per day ?
Drew

capekate

Hi Drew
I never was good with figuring out the best wattage for use with plants etc. But I do have java moss growing very nicely in all my tanks with different types of lighting (all low lights). I keep my lights on the tanks for about 13 hours a day.
Hopefully others that have more knowledge on wattage recommendations will be able to help you further.

mathas

1.5 WPG is on the high side of "low light", probably closer to medium. While it's all subjective, a moderator at PlantGeek posted the following breakdown, which I more or less agree with on tanks with a normal height:

As far as how long to leave the lights on, mine are one for 11 hours a day. I don't have any scientific basis for this, but I would assume anywhere from 8-12 hours would be fine.

GreenMan13

+1. Lower end if you are getting a lot of algae bloom or higher if your plants need more light.

Fla_Larry

pretty much as everyone has said, the general consensus is between 10 & 12 hours per day, some have even gone to adding a "siesta" time period of around 2 hours in the middle, this supposidly disrupts alge growth with out affecting plant development