Lighting For Marines
If you are just keeping marine fish, and don't intend to keep any corals or invertebrates, you can use any standard lighting which comes with the tank, but it would be wise to invest in a better quality tube to reduce algae problems. Corals gain energy from the algae cells which live within their tissues (called zooxanthellae) and these will require an intense light if they are to thrive, so a reef tank will require much brighter lighting.
High intensity 'T5' lightingA normal 1 inch diameter fluorescent tube is referred to as a T8, whilst a thinner half-inch tube is called a T5 (the T rating is just for size) In recent years, high intensity T5 tubes have become more affordable and available and are of good enough quality and intensity to be used on smaller reef aquariums. For most small aquariums up to 45cm (18”) deep, you would need three or four T5 tubes to provide sufficient light for basic corals. These can be a mix of 'white' tubes, giving a bright balanced light, and 'actinic' tubes which provide a better spectrum of light for corals.
Metal halide lampsFor larger or deeper tanks, metal halide lamps are the best option and provide the most intense lighting available for reef aquariums. Because these lights run at quite a high heat they need to be positioned away from the aquarium and in open air. Most halide lamps are designed to hang above the aquarium, meaning they need to be fixed to the ceiling but it is also possible to get light units that can be positioned over the aquarium on a raised stand. Halide lamps can be quite expensive and will represent a serious investment – for a 120cm (four-foot) aquarium you can expect to pay £300-£600 for a good halide lamp. Most halide lamps come with additional actinic tubes to give a better overall wavelength of light for your corals, and these tubes can also be used as night-lights.