Plants and light times

How many hours should the light be on for the plants? I wasn’t putting on the lamp a lot and noticed that my plant, which has been very healthy for months, just started to brown.

I was thinking I can keep it on about 5 or 6 hours a day?

The tank isn’t near any windows.

(Yuji is currently hiding in his coconut. The light doesn’t seem to bother him at all)