The tank in that video has 4 lights over it because it's a very deep tank, 30 inches deep, plus, we wanted to showcase the goosenecks too. The goosenecks hold the light close to the water, so it doesn't give the best spread. If we were to have the lights hanging at optimal levels, we would probably only need 3.
They're awesome lights, gives plants very nice color and great growth.
Here are the 3 18x18x18 cubes that are running amazon suns, as well as our big display (these pictures were taken on veterans day weekend - 2 weekends ago)