When selecting lighting for a marine tank, the first distinction that needs to be made is between a fish only set-up and a fish reef set-up where brighter lighting is required in order to keep corals. Hard corals require more intense lighting then soft corals.
Lighting for Corals
When keeping corals your should attempt to have at least 2-5 watts of lighting per gallon of water. The brighter the lighting the quicker the corals can photosynthesize. If the lighting in a reef aquarium fails too much the corals the algae inside the coral's tissue starts to die leading to the death of the corals.
Light Spectrum
Another consideration when selecting a new lighting system, or when replacing an existing tube is the light spectrum required. To enable photosynthesis to occur aquarium lighting needs to try and duplicate the spectrum of sunlight. The light spectrum of tube is measured using the Kelvin temperature scale, a the noon sky is closest to a 5,500 degrees Kelvin (K) bulb, which is slightly bluish in appearance. The natural habitats of many popular reef aquarium organisms have a bluer light spectrum and a light spectrum around 7100K that is commonly referred to as actinic since deeper water becomes bluer as the water starts to filter out the longer light waves that sit towards the red end of the spectrum. This is important since the range of organisms growing in blue wavelength include stony and soft corals.
T5 lighting
T5 is a new lighting system. The tubes are thinner than conventional T8 tubes and they produce approximately twice the light output of the equivalent conventional "T8" tubes. They require special T5 lamp holders and starter units.
