The quality of light in your aquarium can affect the quality of your aquatic life. Your plants, corals or invertebrates require a correct spectrum and intensity of light in order to survive. When it comes to designing your aquarium you need to duplicate natural conditions as much as possible. This is now easier than ever before thanks to advancements that have been made in lighting technology.
For aquariums that have only fish, artificial plants and decorative wood and/or ceramics then you want a standard or power compact fluorescent system. The lighting system should be between one to two watts per gallon and should be able to stimulate a day-night cycle. Since a fish-only aquarium is a little more forgiving than other it allows you to choose a bulb spectrum that meets your individual preferences. However, don’t use standard hardware store bulbs since they will promote the growth of brown algae.
Then there are freshwater aquariums which typically contain fish, live plants and decorative wood and/or ceramics. For these aquariums you want a standard fluorescent, T-5 HO, VHO, Power Compact or Metal Halide/HQI light bulb. Most freshwater plants come from shallow rivers in Central and South America where they are exposed to the full-spectrum of light. Depending on the plant and the depth of your tank you will need between two and five watts per gallon.
Lastly there are marine reef aquariums which often have fish, invertebrates, corals and live rock. For these aquariums it is best to use T-5 HO, VHO, Power Compact or Metal Halide/HQI light bulbs. Light is a major part of nutrition for many corals and invertebrates, but each individual type requires a dramatic difference in light. Depending on your decorations you will need between four and eight watts per gallon.