The goal is to replicate the natural hours of lighting in nature. From that part of the globe (origin of the fish, etc.) daylight hours are consistently 10-12 hours a day. That being said, you have to take into account the hours of dawn and dusk as the sun giving off light as it rises and sets. The "long hours" of light are great for plants (and that can be reflected in those areas of the world with really long hours, such as Canada, Alaska), but algae loves those kind of hours, too. In the wild algae also thrives along side of the plants. Unfortunately, no one is there to scrape it completely off with the exception of the occassional nibling by fish. In an enclosed system you have to experiment with hours of light to reach that happy medium of enough light for plant growth and too much for algae bloom. Best advice, keep the fish and plants happy with enough light and keep the algae scraper handy.