What type of LED lighting is right for your reef aquarium?
Regardless of the brand, quality or claims made by many light manufacturers (including Kessil, Radion, AI etc.) it is difficult to properly light areas larger than 12" x 12" to 12" x 18" with a single modular or pendant light fixture. When using these lights it is always better to use two or more lights to get proper coverage. Even then you may have difficulties lighting the front and back of your reef aquarium adequately, especially if you have corals placed higher up at the back of the aquarium. You will likely have to raise the lights a foot or more above the aquarium causing annoying stray light in the room. These lights are bright, they just have too small of a footprint.
Think of a small light source to be equivalent to the sun. Even though the sun is massive, bright, and emits light in all directions equally it will always cast shadows unless it is directly overhead. In an aquarium the light is only directly over an area the size of the actual fixture. Therefore any corals (especially branching types) tend to only receive light from one direction/side unless they are directly under the light fixture. A light meter may detect good amounts of light when the meter is facing directly towards the light in an empty aquarium, but as soon as the meter is tilted several degrees or the aquascape and coral casts shadows you will find greatly reduced light levels. Using multiple fixtures, or better yet, using fixtures with larger footprints is the best solution to this problem.
What do we base this statement on? Lots of testing and experimenting! We keep and propagate over 150 varieties of coral in our farm system. Our system includes a 150cm x 150cm shallow grow out tank that allows us to experiment with many types of lighting.
The aquarium pictured below is the side view of a 93 gallon cube aquarium owned by the president of Pets and Ponds, who began keeping and even propagating coral in 1990. It is lit with 6, well spread T5 lights as well as a single 150 watt metal halide, for the light hungry corals at the back. A few 400-450nm LED spot lights were added to get a little extra "glow" out of some of the corals, nothing works better than LEDs for this. Even though he had numerous LED options to choose from he did not use LEDs in order to minimize the drastic shadows and "hot spots" produced by using the popular, small footprint fixtures. However, had larger LED fixtures been available when he set this aquarium up he would have chosen them due to the large footprint and even spread of light they produce.