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If you will not be keeping live plants, macroalgae, or photosynthetic invertebrates, the only lighting you need on your tank is what you’d like in order to view your fish, so you can choose the lighting you like best. However, a tank that looks perfectly illuminated to us can be completely unacceptable to plants, and even what would make for a well-lit planted tank would not be bright enough for most of the photosynthetic marine invertebrates found in reef aquaria.

  • A minimum of 1½ to 2 watts per gallon is needed for planted tanks, with higher amounts depending on the lighting requirements of the plants you keep. For a high-tech setup using CO2 injection and fertilizers, you would use more powerful lighting, up to 4 or 5 watts per gallon. Reef setups usually require 5 or more watts per gallon.
  • Several factors affect the required lighting. Light does not penetrate water easily, and every inch of depth greatly decreases the effective illumination. The use of good reflectors can increase effective illumination by directing more of the light produced into the tank. For a 12-inch-deep tank you can use very high output (VHO) or power compact (PC) lamps, but a depth of 18 or 24 inches requires many more watts per gallon—and probably metal halides—for the same results.

Lighting Types

Not counting regular incandescent lights, which are rarely used nowadays, there are two basic types of lighting for photosynthetic organisms: fluorescent and high-discharge filament lights.

  • NO Lighting: Normal output (NO) fluorescents are regular fluorescent lights. A standard 4-foot bulb is 40 watts. They run off regular ballasts and fixtures and come in a variety of spectra. They are satisfactory only in very shallow tanks.
  • VHO Lighting: Very high output (VHO) fluorescents pack much more lighting power. A standard 4-foot VHO bulb is 110 watts. Special fixtures and ballasts are needed to run these lamps. They work well on tanks up to about 18 inches deep.
  • PC Lighting: Power compact (PC) fluorescents are single-ended, with the tube bent back so that both ends terminate in the electrical connection, and they require appropriate fixtures and ballasts. They are available in a variety of configurations and wattages. The bulbs come in different spectral outputs.
  • HD Lighting: Most high-discharge (HD) aquarium lights are metal halide. These come in both screw-in and double-ended formats and a great variety of wattages and spectra, measured in Kelvins. Because of the intense heat generated by these lamps, the fixtures often include one or more fans, and they are generally hung above the tank to reduce heat transfer to the water. Metal halides are powerful enough to punch through deep water to provide sufficient illumination for photosynthetic reef invertebrates.

Bulb Choice

  • To choose bulbs, you need to consider tank depth and your target organisms. High-light plants, including most red ones, need 3 watts per gallon or more, while low-light plants can get by with 2 watts per gallon or less. For reefs, small polyp stony corals and tridacnid clams require the most intense lighting, 5 watts per gallon or more.
  • All the information you need is on the packaging. Aside from the power of the bulb, which is indicated by the wattage, the spectrum is what you need to be concerned with. A range of spectra, from general lighting to special uses like freshwater planted, full sunlight, and high-blue actinic, are all available for different uses.
  • Many bulbs are rated in Kelvins. This measurement indicates the temperature a theoretical black body would have to be heated to in order to glow at a particular spectrum. The higher the number, the bluer the light, with natural sunlight rated at 5500K. Lower numbers indicate a redder or more yellow light, and higher numbers indicate bluer light. Since blue light penetrates the farthest into water (red penetrates the least), photosynthetic organisms from deeper water need higher Kelvin ratings.

Classic Q&A: New Nano Tank

I recently set up a 12-gallon nano tank. The lighting is a 13-watt compact fluorescent light. Is this enough for a nano reef? What kinds of upgrades do I need to make? Right now all the system contains is live aragonite sand and four pounds of live rock. It has pristine water quality. Any help would be appreciated. Cheyenne Bellows (via email)

The lighting for your nano tank should be selected according to the organisms that you plan to keep. If you aren’t keeping any photosynthetic organisms, the lighting you have should be fine.

If you are keeping photosynthetic organisms, however, you should have full-spectrum, high-intensity lighting. The current 13 watts you have doesn’t seem to provide that for a 12-gallon tank—about 40 watts would be better. Metal-halide lighting would be the best, but this is usually of higher wattage, and it takes a lot of electricity and gives off a lot of heat. For that reason, it can be tricky to utilize metal-halide lighting on a nano tank.

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