Generally 3-4 watts of lighting per gallon are necessary. Lights come in two basic varieties:

• Fluorescent

• Metal Halide

Fluorescent come in a number sub-variations as well:

• Normal Output (NO)

• High Output (HO)

• Very High Output (VHO)

• Power Compact

"NO" tubes are the least expensive and longer fluorescent tubes yield higher wattages. HO and VHO increase the wattage and reduce the number of tubes you need to achieve a desired lighting level. Unfortunately, special ballast kits are required to make them work properly, so the cost is increased. They should have a Kelvin rating that is above 5500K, as that provides adequate coloring that isn’t too yellow. Power compacts are fluorescents that bend back in a tight U shape, so that the length of the tube is effectively doubled and wattage is increased.

The appearance of the tank and fish can be altered by replacing standard tubes with a variety of spectrum colors. If you have the option, choose lighting with two or more tubes. This allows flexibility in the types of tubes that are used at the same time.  Place lights on a simple timer so that the tank receives a consistent 12 hours of lighting per day, which simulates the tropics.  Also allow for some cloudy days by shortening or eliminating lighting some days.  To get fancier, allow more lights to come on in the middle of the lighting period, to simulate the noon day sun.  A Ground Fault Interrupter is always a good idea with electrical equipment that can come in contact with water.

Metal Halides are very strong incandescent lights. They are excellent at ensuring adequate lighting for delicate corals. Their downside is that they are so powerful they cannot be placed close to the water and overheating of the water is often a problem.  They do seem to provide better photographic lighting.

Fish Only

For beginners in a FO (fish only) tank, full spectrum normal output "NO" fluorescent lighting will be fine. 

Reef Tanks

Most standard lighting canopies have insufficient lighting for corals and invertebrates. They need strong full spectrum.  Actinic blue fluorescent tubes are currently also very popular in combination with full spectrum lighting, but there isn't a lot of evidence that these are necessary. Alternately, a metal halide can be used. It is better in a reef tank to ensure that the lighting canopy does not enclose the surface area. If you make changes to the lighting in a reef tank, this should be done over night, as changes in coloration and intensity will cause a hardship to corals and invertebrates. 

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