I agree with both members above. The tank light can be somewhat harmful to many forest fish, and that is much more an issue if it is bright.
In total darkness, which means pitch black at night with absolutely no ambient light in the room, most fish will "sleep" or rest, inactive unless suddenly startled. Other species like many catfish will be active during such darkness. A regular schedule of "day" and "night" replicating their habitat is best, but the "day" does not have to be very much as others noted. The fish have an internal clock of sorts, called the circadian rhythm--actually all animals including humans have this, and there is something similar in plants--and consistency of "day" and "night" and in between dusk and dawn times is important.
When the tank light is again operating, be careful as it might be something of a shock for the fish after two-plus weeks of no overhead light. No idea on what species you have, but any sudden bright light can stress most fish even when turning on the light in the morning (always have ambient light in the room when tank lighting comes on and goes off, and keep those times the same each day to not mess up the circadian rhythm.
