If you have differant types of plants in your tank you should also take these into consideration, some plnts require lots of light, some require less light, but you can find this out when buying them. If you have just fish in you tank, then you will want to see them. so your lights need to be on when you are relaxing at home. I think if you stick between 8-10 hours you shouldn't be far wrong. But if you do have plants check on there requirements.