One of the most important pieces of hardware on a reef aquarium is the lighting system. Most of the invertebrates kept in a reef aquarium rely on the byproducts of photosynthesis for most of their nutrients. Without the proper lighting system, these invertebrates will slowly waste away and eventually die.  The problem is selecting a lighting system from the bewildering array of choices.  

Selecting the type of lighting system for your reef can be quite confusing. If you ask 3 aquarist what type of lighting you should buy, you get 4 answers. Knowing what type of animals you're ultimately going to place in the aquarium is the first step. Some corals, like small polyped stony (SPS) corals, require very intense lighting. At the other end of the spectrum we have soft corals, which still require a good amount of light, but less than SPS corals. We generally measure light intensity by watts per gallon, where lower light levels may be 3 watts/gallon and high levels would be in the range of 5-7 watts/gallon. 

In addition to light intensity, we also must decide on the color temperature of lighting. The color temperature of lighting is measured in Kelvin and determines what color light the bulb emits. The lower the Kelvin rating of the bulb, the more yellow the light appears. A bulb with a rating of 4300K would cast a yellowish light over the reef. This type of bulb is generally used with fresh water planted aquariums. The higher the Kelvin rating, the more whitish-blue the light will appear. The most widely used bulbs for reef aquariums are 6500K and 10,000K bulbs, but there are also 12,500K and 20,000K. The former are used to replicate the intense light of shallow water conditions and the latter are used to simulate deep water environments since the light appears very blue. Knowing the habitats your animals come from is important to determining the color temperature and intensity of light to use.  

Once you've determine the intensity and color temperature of light you're inhabitants require, you then need to select the type of bulb to use. Below I've created a simple chart listing each lighting "genre", and their advantages and disadvantages. Hopefully this will help you make an informed decision of what type of lighting system best meets your needs.