Lighting Intensities for Reef Tanks: Rules of Thumb
Veterinary & Aquatic Services Department, Drs. Foster & Smith

Q. I am planning on setting up a 55-gallon saltwater reef aquarium. I've heard differing opinions as to how many watts of light to provide. How much and what type of lighting is required?
A. Lighting really depends on the needs of your aquarium inhabitants. Saltwater reef aquariums are commonly defined as containing at least one pound of live rock per gallon of water and an array of invertebrates, corals, and fish. However, some reef aquariums contain non-photosynthetic invertebrates and corals which require absolutely no illumination. When choosing the lighting for your aquarium, first be sure you know the basic light requirements of your selected aquarium inhabitants. (See individual species descriptions included on to learn about their unique lighting requirements.)

Invertebrates and corals are classified as low-light, medium-light, and high-light according to their nutritional needs and their ability to photosynthesize. These different classifications require varying lighting types and wattages. The following recommendations are for an aquarium 24" deep or less:

  • Low light  €“ Use standard fluorescent lighting of 1-2 watts per gallon.
    Please note: many low-light corals and invertebrates have special feeding requirements and can be difficult to maintain.

  • Moderate light  €“ Use power compacts or VHOs (Very High Output) fluorescent bulb systems providing 2-4 watts of light with an equal mix of daylight and actinic spectrums.

  • High light  €“ Use intense metal halides supplemented with power compact or VHO actinic bulbs. Provide a total of 4-8 watts of light per gallon, and choose a metal halide bulb with a spectrum that suits your color preferences. Please note: these systems create a large amount of heat, and typically require the addition of cooling fans and a water chiller.

When designing your lighting system, remember to consider costs  €“ not only the initial cost of the lighting equipment, but also subsequent operating costs and additional equipment which may include: cooling fans, water chiller, or a specialized canopy or hood.

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