What Kind of Aquarium Light Should I Buy?

Part of planning an aquarium is determining the type of light you will need to illuminate your underwater pets. The choice is easier to make for tanks that will hold only fish, because their needs are not complex. But for hobbyists who want to grow live plants in their fish tanks or who would like to recreate a coral reef, the lighting choices are more varied. Those aquariums require strong light and the right type of bulbs to look their best.

  1. Fish-only Tanks

    • For an aquarium that will hold only fish, the primary option for hobbyists is the choice to use fluorescent or incandescent bulbs. The fish tank setups sold at pet stores often come with a hood that includes a built-in light fixture. Incandescent lights are less expensive than fluorescent bulbs, but they produce a lot of heat that may raise the tank's water temperature. Fish-only tanks need only about one to two watts of light per gallon of tank capacity.

    Planted Aquariums

    • Hobbyists often use specialized fixtures and bulbs to provide the intense light that plants need to grow in an aquarium. A rough rule of thumb is to provide at least 2 to 3 watts of light per gallon of tank capacity, but deeper tanks need more wattage to allow the light to penetrate to the tank floor. Because so much light is needed, many hobbyists chose to use compact fluorescent bulbs. These bulbs produce bright light without the heat of incandescent bulbs. The color of the light is also important. Bulbs are measured by color temperature expressed in degrees Kelvin. Lower temperature bulbs provide light that appears more red, while higher temperature bulbs providing light that appears more blue. Aquarium plants grow well under lights that are close to natural sunlight at noon, about 5,500 to 6,500 degrees Kelvin.

    Reef Aquariums

    • Marine tanks that feature saltwater fish and live coral need even stronger light than planted tanks require. Corals and invertebrates, like sea anemones, also use photosynthesis to grow, just like plants. A general rule of thumb is to provide 4 to 8 watts of light per gallon of tank capacity. The color temperature of the bulbs should be around 10,000 degrees Kelvin, which mimics the blue-tinted light normally found in an ocean reef.

    Specialty Options

    • Metal halide pendants, which are mounted to the ceiling and hang directly over the tank, can provide dazzling light for both planted tanks and marine reef tanks. The effect of a strong light source above the water gives the tank a shimmering look. These bulbs get very hot, so good ventilation is essential. In marine tanks, hobbyists can also use actinic bulbs as part of their light setup. These intensely blue lights, around 50,000 degrees Kelvin, help certain corals to grow. They are usually used in conjunction with lighting at a lower color temperature, to provide balance.