There are several types of lights encountered in the saltwater hobby. Each type of light has their positives and negatives, listed here are the three main type of lights encountered in the hobby.
LED (Light-emitting diode). This is the newest type of technology to be occurring in the lighting industry. LED can be encountered in miniature saltwater aquariums to very large aquariums. LED have many advantages such as being able to have a more focused spectrum, lower energy consumption and lower temperature. A focused spectrum gives the ability to be able to more precisely choose a certain range. Some can argue this narrow spectrum can be bad for corals, but with the right choice of LED, one can provide a healthy spectrum of light for corals to thrive. Due to LED focused spectrum and optics, if not combined and not position properly one can cause light effects that for some might be desirable and to other undesirable. These effects include shimmering, incomplete color blending and focused beams. Almost all type of corals have been grown successfully under LED lighting.
Metal Halide For larger aquariums, hobbyist are more likely to encounter metal halide. These lights are very intense and cover a wider range of spectrum than a single LED would cover. The benefits of metal halides are that they have been on the market for much longer and many type of bulbs and information can be readily found. The type of light produced by a metal halide is very bright and produces a unique tone of color. All types of corals can be grown under a single metal halide light but care must be taken at the top of the tank, because corals can easily receive to much light and cause bleaching. Some disadvantages of metal halide are that they produce a tremendous amount of heat, consume large amounts of power and are usually unsuitable for very small tanks.
Power Compact (PC) Power compact are used for smaller to mid sized tanks and sometimes large tanks. They pack a lot of energy in a small space. For this reason they are used in smaller tanks to mid size tanks. Two very common types of PC bulbs are encountered: Actinic, 420nm/460nm and Daylight bulbs. Actinic are used to give that pop/fluorescent color that certain corals emit. Actinic produces a very blue light. 420nm/460nm is also blue but it is mainly used to provide the proper spectrum that the symbiotic organisms in the corals require. Daylight is added to produce a more pleasing natural tone to the light. Hobbyist will vary the specturm to produced a desired look. PC’s are used in several starter kits that are sold online and at retail stores. These bulbs produce less heat than metal halides but more that LED’s. Some disadvantages are that several bulbs are needed to provide high enough intensity to grow more light demanding corals.
In summary, the main objective of lighting is to produce light that is beneficial to the organisms inside corals, and to produced a desired color that is pleasing to the hobbyist. The intense and fluorescent color that coral emit are due to the algae that inhabit the tissue of corals. These algae are collectively known as Zooxanthellae. Zooxanthellae are photosynthetic and symbiotically feed the coral. Under certain lighting, like the ones mentioned above, cause these Zooxantehllae to fluoresce giving the bright color that corals emit.