i am running my bulbs for about 15ish hrs a day, currently it's a 120watts of total lighting, 1 60watt full spectrum, the other a 60watt actinic blue, and the tank takes about 2.5- 3weeks to get covered in algea, before the plecto went in. so if you shave the time down to 10-12hrs, it should slow the growth down some. however this is hard to say for certain, many things factor into algea growth, dissolved co2
levels, lighting quality, nitrates in the water, ectand there are a few more ways to limit the algea growth.
a) since you have the lighting.. add some plants into the tank, but just don't go overboard, 2-3 small plants should be just enough. the surplus of nitrates in the tank, will be absorbed by the plants and not the algea, thus limiting the growth of the algea.
b) get something that eats algea, a plecto is a great candidate, or even a snail, a nice large apple snail chugging along the gravelbed is a great sight to come home from work too.
c) get some algea-cide and put that in the tank, every month, and that will kill the algea.
now you said something about ambient lighting in the tank's room, if the ambient lighting is sunlight, it won't limit much if any algea growth. your new lights try an mimic the sun's nature rays.