Virtually all marine systems are in need of an artificial light source, both for the enjoyment of viewers and the health of the viewed. Natural sunlight provides the elusive perfect spectrum that advanced reef aquarists crave, but it has severe limitations for most of us. Aquariums placed in direct sunlight will quickly overheat unless their waters artificially chilled. During winter months in northern latitudes, there aren’t enough hours of sunlight in the day to keep marine creatures alive and thriving. Finally, the sun doesn’t shine when most of us have our treasured viewing hours - in the evening.

It follows that one of the most significant investments in a marine system is the lighting. I’ve seen setups in which the lighting equipment cost more than the rest of the system combined.

This emphasis doesn’t seem unreasonable. After all, humans are visually oriented beings; it makes little sense to have beautiful fishes in a wonderful aquascape that is poorly lit. Additionally there are photosynthetic needs in systems that have more than fishes in them, and even piscine vertebrates require light energy (as we do) for good health.