The reason people with Kessils "supplement" with LED bars is to get some diffuse light into the tank, not because they're underpowered/don't grow coral. Kessils, because of the Dense Matrix LED array, lens, and reflector, make a point light. That is, all of the light coming from a single small point, similar to the Sun in Space. Radions make the lightsource larger, and therefore softer, creating a more diffuse light with softer shadows. The sunlight reaching the reefs is actually a mixture of the two types of light (Sharp collimated light and Diffuse light). The light from he sun diffuses through our atmosphere, clouds, water vapor, and then diffuses further once the water and particles in the water bounce the light in all directions.