it depends on the plants you have and how much you want to dose ferts and co2
. if you're not getting algae or green water and the plants are growing then i'd say you're not getting too much light. just remember that the more light you have the faster your plants grow and use the nutrients which means the more you have to dose and trim the plants and the more electric you use.
i would try to simulate the sun a little better and turn the second light on a few hours after the first one and turn it off a few hours before the other one. you could probably cut back to ten hours and save some electric. just watch your plants and tank and it will tell you if it needs more or less light.