[ReschM]

I don't have a tank yet but certain things are given on this planet. First, the earth rotates, allowing gradual increase and decrease in lighting. Second, out in the ocean where reefs are located, there are no trees, mountains or man made objects to block the suns rays. So yes there is a gradual increase and decrease of light but the change is much more sudden then what we are used to, Maybe not as sudden as flipping a switch but fish around the world have survived the light on, light off life style for years.