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How to Light a Saltwater Aquarium

How to Light a Saltwater Aquarium

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While tanks and chillers and protein skimmers are expensive, it is the lighting that can really add up, especially in a saltwater aquarium. In this guide, we’ll discuss the major lighting options and make some recommendations for the aquarium system you are planning.

Natural Sunlight

Isn’t the sun’s light sufficient to support reef life in the wild? Then why can’t I simply use the sun’s light for my reef aquarium? This is a common question with a common answer: don’t do it.

If you live in the Tropics, are not interested in viewing your tanks at night, and have an effective strategy for cooling the tank, maybe you could safely rely on the sun for your livestock’s lighting needs. For the rest of us, the days are too short, our desire to view our aquaria when we are home in the evening is too strong, and our pockets are simply not deep enough to purchase and run the size chiller we would need to keep the aquarium temperature low enough to sustain life. So we turn to artificial lighting.

Beaming Fluorescent Light

Fluorescent lights are the most commonly used lights in the aquarium hobby. They have the advantage of being less expensive than other types of lighting. They also have a low operating cost and do not emit as much heat as other bulbs. Having said that, most fluorescent lights alone are not appropriate for a marine aquarium. The only florescent bulbs that can provide the necessary light for the health of your animals are full-spectrum fluorescent lights (not broad spectrum and not wide spectrum—full spectrum) that are also high-intensity fluorescent lights.

When purchasing a full-spectrum fluorescent bulb for your marine aquarium, you will have several options to consider. Full-spectrum fluorescent lights are rated with color temperature in Kelvin (K), luminosity in lumens, and a color rendering index or CRI. A decent, full-spectrum (daylight) fluorescent bulb will be at least 5,500 K (preferably between 6,000 K and 7,000 K), 2,000 lumens, and have a CRI over 80 (better if it’s over 90). A high Kelvin-rated fluorescent bulb will be between 10,000 and 20,000 K.

Most retailers simplify the process of choosing fluorescent lights by offering some variation on two general categories:

Metal Halide (MH) and Hydrargyrum Quartz Iodide (HQI) Lighting

Metal halide (MH) lights work on a completely different principle than fluorescent lights and provide some of the strongest possible lighting for a marine aquarium. Hydrargyrum quartz iodide (HQI) lighting is a variety of MH lighting. If you intend to keep corals with very high lighting requirements, metal halides are probably going to be your first choice, especially when combined with actinic or other fluorescent lighting.

MH lights are also ideal (even necessary) for deep tanks, as they are one of the few lighting options that can penetrate to 60 centimeters (24 inches) or more in depth. Some reef aquarists not only consider MH/HQI lighting the gold standard in reef keeping, but even required equipment. Unlike fluorescent lights, metal halides do produce a lot of heat (so much so that most reef tanks using metal halide lights often need to use a chiller). Appropriate ventilation, however, can go a long way to dissipating the heat. MH/HQI lights are also expensive to purchase and, at least on the surface, costly to operate. In reality, MH/HQI lights are more cost-effective than many other lights considering the life expectancy of the bulbs and the useful light per watt. An entire book could be written on aquarium lighting, so we suggest you use our comments as a jumping-off point for doing your own research.

LED Lighting

LED lighting may be one of the most exciting new frontiers in aquarium equipment. These lights don’t produce the same heat, and they cost significantly less to operate. In addition, the bulbs last much longer than metal halide bulbs or fluorescent bulbs. Unfortunately, LED lighting is still cost-prohibitive for many people, but as the technology advances, the cost is coming down and the quality is going up. LED lights are something to keep your eye on.

Lunar Lights

LED lights are frequently used for moon lights or lunar lights that can simply create a cool nighttime effect or actually stimulate various behaviors in certain species. They can either be set up to simply turn on and then turn off, or they can be run by a controller to simulate actual lunar cycles.

Plug-and-Play Lights

While we tend to not like plug-and-play reef kits, we are more supportive of some plug-and-play lighting systems. There are many of these on the market these days, and they allow you to purchase a single unit that will cover all of your bases without needing to be an electrician. While you can certainly build your own lighting system from the ground up, commercially available units can provide you with the true 24-hour lighting experience with almost no hassle. Many of these systems incorporate metal halide lights, various fluorescent lights, and LED lunar lights all packaged in a neat housing with built-in ballast, on-off switches for each light, and integral cooling fans. These lighting systems are not cheap, but they do take the headache out of piecing a lighting system together.


We strongly recommend you run your lights on a timer(s). The plug-and-play kits we described above sometimes come with an integral timer, or they ship with external timers. If your lights don’t come with timers, get them. An alternative is to use an aquarium controller to control your lights. However you do it, you will want to have your lights on between 12 and 14 hours per day.

If you use a combination of lights, you could program your actinics to come on for an hour or so before the full spectrum fluorescents or metal halides come on, and then have the full spectrum fluorescents or metal halides go off about an hour before the actinics go off. In this way, you mimic dawn and dusk. If you have LED lunar lights, you can also set these up to simply come on at night or to mimic the phases of the moon. Regardless of how you set up your system, remember that lighting is critical, and so is consistency from day to day.

The best advice for a beginner aquarium keeper is to spend good money on lights; and don’t be surprised if your lights are the single most expensive piece of equipment you purchase for your saltwater aquarium—they are that important. Good luck!

From The Complete Idiot’s Guide to Saltwater Aquariums by Mark W. Martin and Ret Talbot