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Following is an excerpt from "Lighting Choices for the Marine Aquarium," by Gregory Schiemer, which appeared in the March 2000 issue of Aquarium Fish Magazine. To see the entire article, please click here.

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Lighting Choices for the Marine Aquarium

The working title of this article was "Lighting Choices for the Reef Aquarium." I then got to thinking that all tropical marine aquariums, whether they include live corals or not, should be constructed and maintained as reef aquariums. The word "biotope" has become a popular term lately in the aquarium hobby, and with good reason. Animals do best and look their best when maintained in a captive environment most similar to their natural environment. The majority of tropical marine fish come from areas of coral reefs, so their captive habitat should be set up to mimic that environment.  If you were keeping rift lake cichlids you would assemble an aquarium that included rocky outcroppings and alkaline water. Amazonian angelfish look best in a tall tank that includes swordplants, replicas of submerged tree roots and driftwood. So, when it comes to keeping coral reef fish, the aquarium should contain - at a minimum - structures of calcareous rocks (live reef rock is best) and possibly coral sand as a substrate. The water quality should be maintained within natural reef parameters.

The decisions regarding lighting should be based upon the same criteria. Lighting is an important aspect of the natural environment of fish. I've seen it written that lighting is unimportant if an aquarist intends to keep only fish. It's often recommended to use just enough light to view the fish.  Based upon my experiences, this is not only unnatural (most tropical marine fish come from areas of clear water and bright sunlight), but also unhealthy. Insufficient light can be a stress factor and has been implicated in "head and lateral line erosion." The physical dimensions of the aquarium and the nature of its inhabitants should dictate the type and quantity of lighting.

Marine aquarists are faced with a bewildering array of choices when it comes to lighting. Before we get into choosing the most appropriate lighting scheme for your aquarium, let's take a look at what's available in lighting and the characteristics of each type.

Power compact (PC) lamps are the latest addition to the aquarium lighting market. They are fluorescent lamps that can best be described as standard fluorescent tubes that are folded back on themselves to form a tight "U" shape. The result is a lamp with a relatively small footprint but with higher output compared to similarly sized standard fluorescent tubes.  Also, unlike traditional fluorescent tubes, PCs are single ended. They have two or four pins at one end of the lamp and fit into a unique lamp holder.

PC lamps require special ballasts. These ballasts can be traditional electromagnetic or the newer (and more efficient) fully electronic variety. Most of the better fixtures on the market use small electronic ballasts. For a list of the most popular PC lamps available in the hobby, see Table I below.

PC lamps and fixtures are sold by many companies in numerous forms and configurations. They were first popularized for the aquarium hobby by Custom Sealife, but are now available from numerous manufacturers. Some of the prominent manufacturers and their offerings include:

  • Aquarium Systems - 55-watt PC striplights in one and two tube configurations.
  • Custom Sealife - Replacement lamps, full hoods, retrofits, and combination metal halide/PC hoods and retrofits.
  • Hamilton Technology Corporation - Full hoods, retrofits and combination metal halide/PC hoods and retrofits.
  • IceCap, Inc. - Replacement and do-it-yourself electronic ballasts for 28-, 55- and 96-watt PC lamps.
  • Osram - 55-watt PC lamps.
  • Panasonic -  9-, 13-, 55- and 96-watt PC replacement lamps.
  • Perfecto -  55-watt PC striplights in one and two bulb configurations.

Some of the benefits of PC lamps include:

  1. They are relatively cool compared to metal halide bulbs
  2. They are compact in size
  3. They are energy efficient, compared to standard fluorescent and very high output fluorescent tubes run on conventional ballasts
  4. The lamps and parts are generally available within the aquarium trade.

Some of the downsides of PC lamps include:

  1. Replacement lamps are relatively expensive compared to standard and very high output fluorescent tubes
  2. Their useful life is not appreciably longer than standard and very high output tubes, especially if they are used in conjunction with electromagnetic ballasts
  3. Limited sizes, color temperatures and wattages compared to standard and very high output fluorescent tubes
  4. Limited availability. PC lamps and parts can be hard to find outside the aquarium industry.

For a thorough discussion of PC lighting, including a wealth of do-it-yourself information, you can refer to the article by Sanjay Joshi in the April 1999 issue of Aquarium Frontiers (

Very high output (VHO) and high output (HO) fluorescent tubes are similar in size and appearance to standard regular output fluorescents, but use a heavier filament that enables them to be driven at much higher wattages. The result is, of course, more light output in the same amount of space.  These lamps were initially popularized in the aquarium hobby back in the 1980s. They were the first lights used over reef aquariums that truly enabled aquarists to maintain some of the photosynthetic corals in captivity for the first time. They are still very popular today used alone or in combination with metal halide bulbs over reef aquariums.

HO lamps differ from VHO lamps in that they use less wattage and produce less output. They fall between regular output and VHO lamps. HO lamps are rarely used or offered for sale today for the aquarium hobby. VHO lamps can be driven by conventional "tar" ballasts (rated for VHO lamps), but are much more useful and efficient when driven by electronic ballasts (e.g., IceCap).

  • VHO fluorescent lamps are offered in many sizes and wattages. Some of the more popular types used by aquarists are listed in Table II.
  • VHO fluorescent lamps and lighting fixtures are sold by many companies in many forms and configurations. Some of these manufacturers include:
  • Coralife (Energy Savers Unlimited, Inc.) - Fixtures in combination with metal halide lamps, retrofits in combination with metal halide lamps and replacement lamps (10,000 K).
  • Duro-Lite Lamps Inc./Duro-test Corp. - Vita-Lite VHO daylight and actinic lamps.
  • Hamilton Technology Corp. - VHO fixtures, combinations with metal halide lamps, retrofits and replacement lamps.
  • IceCap, Inc. - VHO electronic ballasts (IceCap), hoods and retrofits.
  • Ultraviolet Resources International (URI) - Replacement fluorescent lamps.
  • Ultralife: Electronic VHO ballasts (Sun Seeker) and replacement lamps.
  • Voltarc - Replacement lamps.

Some of the advantages of VHO lighting compared to other forms of aquarium lighting include:

  1. There is a large choice of lamp styles and sizes to fit every possible aquarium configuration
  2. VHO lamps can be very efficient and long-lasting (up to 12 months) when used with electronic ballasts
  3. VHO lamps are relatively inexpensive on a dollar per watt basis compared to metal halide bulbs and PC lamps
  4. VHO bulbs, ballasts and associated hardware are available from many sources.

Some disadvantages of VHO lighting include the following:

  1. The tubes need to be changed frequently (every four months), and there is a quick drop-off in output when used on conventional ("tar") ballasts
  2. Conventional ballasts get very hot
  3. SOME VHO electronic ballasts can be finicky (e.g., electrical interference problems, sudden shut-offs, unexplained breaker trips, blown fuses)
  4. VHO electronic ballasts are expensive.

Metal halide and HQI bulbs emit a point source of light, unlike fluorescent lamps in which the light output is spread over a tube. Metal halide bulbs have single-ended screw bases in both standard and "mogul" sizes. HQI-type metal halide bulbs have pins on both ends of the bulb that "snap" into a holder. HQI bulbs must be used in conjunction with a glass ultraviolet (UV) shield. Standard metal halide bulbs have integral glass shrouds like standard incandescent bulbs that allow them to be used unshielded. Both metal halide and HQI bulbs operate on a range of high-voltage ballasts. There are conventional "core and coil" ballasts and newer electronic ballasts. The ballast must be tailored to a specific wattage bulb for it to operate properly.

Coralife (Energy Savers Unlimited, Inc.) first popularized the use of metal halide bulbs as an alternative source for reef aquariums back in the early 1990s. They introduced the first daylight color temperature metal halide bulbs (4300 Kelvin [K] and later 5500 and 6500 K bulbs) for aquarists. Originally only 175-watt bulbs were available to hobbyists; today there are numerous choices in metal halide lighting.

Some of the common wattages and color temperatures include:

  • 100-watt - 5500 K from Venture/Coralife
  • 150-watt - 6500 K by Iwasaki, 10,000 K HQI from Red Sea and Aqualine-Buschke
  • 175-watt - 6500 K by Coralife, 10,000 K from Coralife, Hamilton, and Aqualine-Buschke, 20,000 K from Coralife
  • 250-watt - 5500 K by Coralife, 6500 K by Iwasaki, 10,000 K screw base from Coralife, Hamilton and Red Sea, 10,000 K HQI from Red Sea and  Aqualine-Buschke, 20,000 K from Coralife
  • 400-watt - 5500 K by Coralife, 6500 K from Iwasaki, 10,000 K from Coralife, Aqualine-Buschke and "German," 20,000 K from Coralife, "German"
  • 1000-watt -  5500 K by Coralife, 10,000 K from Red Sea, Aqualine-Buschke and "German."
  • Metal Halide fixtures and bulbs are sold by many companies in many configurations. Some manufacturers combine PC, VHO and regular output fluorescents with metal halide bulbs. The major manufacturers include: Coralife (Energy Savers Unlimited, Inc.), Hamilton Technology Corporation and Custom Sealife.

Metal halide lighting offers a number of benefits.

  1. There is a wide choice of lamps, configurations and styles
  2. Parts and bulbs are readily available at many places in and out of the aquarium trade
  3. It is an efficient source of lighting
  4. Metal halide bulbs are long lasting. Some bulbs can be kept in service in excess of one year
  5. It is the only option that features a point source of light, which is most similar to the sun. The glitter lines created by this type of lighting are natural and aesthetically appealing as well
  6. Metal halide bulbs are the best choice for obtaining high-intensity lighting over a small space and to satisfy the needs of certain reef crest small-polyped scleractinian (SPS) corals.

Some of the drawbacks to metal halide lighting include:

  1. Metal halide fixtures and bulbs are expensive
  2. The ongoing costs of electrical use and bulb replacement are very high
  3. Metal halide bulbs get very hot and must be ventilated. Even with ventilation they tend to raise the temperature of the aquarium by a few degrees
  4. Some electronic ballasts designed for metal halide bulbs can be finicky
  5. The large external ballast boxes and wiring associated with these bulbs are difficult to hide and conventional (non-electronic) ballast boxes also get very hot
  6. There is some incompatibility of ballasts, even with bulbs of the same wattage.

I've included standard fluorescent lighting in this treatise because they are still the most popular and widespread of choices for aquarium lighting. Some of the newer T-8 fluorescent tubes and fixtures, when combined with electronic ballasts, make attractive and efficient alternatives for marine aquarists interested in maintaining a fish-only reef aquarium. Their compact size and efficiency rival that of PC lamps.

The strong points of regular output fluorescent lighting include:

  1. They are available in a wide array of color temperatures and lengths
  2. Parts and replacement tubes are easily attainable both in and out of the aquarium trade
  3. They are inexpensive and cool running
  4. They are efficient
  5. They are useful as dawn/dusk lighting when combined with metal halide bulbs.

They also have some weaknesses, which include:

  1. They are generally insufficient for use over reef aquariums containing photosynthetic invertebrates
  2. They take up a lot of space relative to their output. They require many tubes over the length of the aquarium in order to get sufficient light to maintain photosynthetic invertebrates.

There are no hard and fast rules when it comes to choosing lighting for the marine reef aquarium. I've seen successful reef tanks using all the forms of lighting detailed in this article. One common recommendation is to use between 3 and 5 watts of light per gallon over the typical reef aquarium. This actually isn't a bad recommendation. I would recommend using an absolute minimum of 3 watts of fluorescent lighting per gallon over the typical fish-only reef aquarium.

When using fluorescent lighting it is important to span the entire length of the aquarium with lamps. For example, to light a 4-foot long aquarium, you would use lamps totaling 48 inches in length. These can be single lamps or a combination of shorter lamps.

At the other end of the spectrum, I recommend a mix of metal halide and fluorescent lighting totaling over 5 watts per gallon for a reef aquarium dominated by SPS corals. If you have an unusually shaped tank, you may need to modify these recommendations. For example, I would use a metal halide pendant light totaling 5 watts per gallon to light a tall narrow tank such as a hex-shaped aquarium, especially if I planned to maintain photosynthetic invertebrates at the bottom of the aquarium.

Bulbs and lamps can vary significantly in terms of efficiency, longevity and aesthetics. Choosing what's best for your aquarium can be a daunting task. My suggestions are to read as many independent reviews on lighting as possible, such as this article and those that have appeared in Aquarium Frontiers, and to look at other successful reef aquariums. In this case a picture is truly worth a thousand words. If you can see a successful aquarium first-hand and the look appeals to you, then you might want to emulate that lighting scheme.

Personally, I've had good long-term experiences with the Iwasaki 6500 K series of metal halide bulbs in the 250- and 400-watt sizes. They are my bulbs of choice in those wattages. I combine VHO lamps with these metal halide bulbs to simulate dawn/dusk and to add a blue tinge to an otherwise harsh white light.

The new 10,000 K 250-watt HQI bulbs have been getting glowing reviews and are worth considering as well. If they are similar to the other 10,000K HQI bulbs originating from Germany, they should offer a crisp blue-white light and good long-term performance. The downside to these is that they require a specialized ballast to operate properly.

The Aqualine-Buschke/Hamilton 175-watt 10,000 K bulbs are my personal favorites in the 175-watt metal halide group. They offer a good compromise of aesthetics, efficiency and longevity.

I use 150-watt 10,000 K German HQI bulbs over small reef aquariums and freshwater-planted tanks with good success as well. The 10,000 K HQI bulbs are relatively expensive and not widely available, but the pleasing blue-white light and long-life are appealing characteristics. Also, because the HQI bulbs are physically smaller than standard metal halide bulbs, they can be built into small and fashionable fixtures.

When I choose to use fluorescent lighting I prefer VHO lamps driven by IceCap electronic ballasts. This is a cool-running and efficient combination. As for the lamps themselves, I've had the best experiences with the Ultraviolet Resources, Inc. (URI) brand. URI lamps have been consistent performers and are high quality. I've used URI actinic, daylight and actinic/white lamps with equally good results.

Regardless of the type of lighting you choose, it's necessary to perform routine maintenance. One aspect of maintenance is replacing lamps and bulbs. It's important to develop a regular schedule.

Here are a few of my suggested guidelines:

  • Regular output, PC and VHO fluorescents can have useful lives in excess of 12 months when run on electronic ballasts. My suggestion is to replace them annually.

  • Regular output, PC and VHO fluorescents that run on standard core and coil ("tar") or electromagnetic ballasts have a considerably shorter useful life. In this case I suggest replacing regular output and PC lamps every nine months and VHO lamps every six months.

  • Metal halide bulbs are a mixed bag because so much depends upon the individual bulb or bulb/ballast combination. The replacement schedule is also affected by the adaptability of the animals (e.g., SPS corals and Tridacnid clams are generally less forgiving of insufficient light). Some of the work done by Sanjay Joshi and Richard Harker suggests that the daylight metal halide bulbs (e.g., Iwasaki 6500 K series) can be used well in excess of one year, but the high-temperature "blue" metal halides (10,000 K and 20,000 K German and Coralife) lose a significant percentage of their useful output inside of one year. My general suggestions are to replace the high temperature metal halide bulbs every nine months and the daylight bulbs annually. You can get more detailed information on this topic by referring to the following issues of Aquarium Frontiers:

  • It's important to never replace all the bulbs/lamps at one time. It could shock photosynthetic animals. The stress of this shock can lead to an expulsion of zooxanthellae (symbiotic dinoflagellates) and ultimately death. It's best to stagger the replacement schedule so that bulbs and lamps are replaced three months apart.

  • I can't overemphasize the importance of keeping bulbs, lamps, reflectors, shields, tank covers and tank braces clean of salt and dust. When these are dirty they can markedly reduce light output. The cleaning of these items should be part of a weekly maintenance routine.

  • Ballast boxes for all types of lighting can get very hot and operate at high voltage. It is essential that they are kept clean and well ventilated. Saltwater and salt dust are good conductors of electricity. It is highly recommended that all ballasts be plugged into ground fault circuit interrupter (GFCI)-protected outlets. In the event of a short, which can occur if water is splashed onto a ballast box or lamp holder, the circuit breaker will immediately trip. This will protect both you and the electrical equipment. GFCI breakers are required by many building codes for areas where water has the potential to meet electricity.

  • When using any high-intensity lighting in an enclosed hood it's imperative that the enclosure be vented in some fashion. Most prefabricated hoods for PC and metal halide lighting come with one or more built-in fans to dissipate heat. These fans should be checked daily and cleaned monthly. If dust is allowed to build up unchecked the fans will eventually stop working.

  • As with all maintenance routines, it's a good idea to keep a log. At a minimum you keep track of the dates that bulbs are replaced. I use small stickers with dates indicating when the bulbs were put in service and attach these directly to my fixtures. It's one of the many aquarium-related uses that I've found for my Brother P-Touch labeling system.

One of the best investments you can make in your lighting system is a good reflector.  The “reflectors” in many older fixtures were simply created by painting the inside surfaces with flat white paint. Over time this paint fades, discolors and peels.

Covering the inside of your light hood with a new "specular" (mirrored) aluminum reflector (e.g., Digital Ocean's Spider Light) can increase light output dramatically. Replacing a reflector is certainly within the ability of even the most amateur of do-it-yourselfers. For more information on the benefits of reflectors see Richard Harker's article in Aquarium Frontiers: (

Electronic ballasts are another useful upgrade. Although they are costly, the gain in efficiency and longevity of the lamps will repay for the cost of the ballast in a relatively short period of time. I personally would not operate VHO fluorescent lamps without electronic ballasts. I don't consider VHO lighting a viable alternative when used with "tar" ballasts. Ballast upgrades can also be a do-it-yourself project, but I would suggest deferring to a qualified electrician if you don't have the basic experience and skills in working with electrical wiring.

One last useful device to consider is a light timer. As important as light intensity is, duration is equally critical for the health and well being of all marine aquarium inhabitants. It too is part of our attempt to simulate natural conditions. I run VHO actinic fluorescent lamps for a few hours before and after my main metal halide lighting to simulate periods of dawn and dusk. It's not necessary to mimic the actual local times of dawn and dusk - simply keep the aquarium on a regular schedule. Because I work during most of the daylight hours, my main metal halide lighting doesn't come on until late afternoon. By the time I get home in the early evening my aquariums are at the peak of the lighting cycle. I don't begin the dusk phase until 10:30 p.m. The total photoperiod is 13 hours. The peak lighting period is eight hours long.

There are many variations of light timers sold in the aquarium marketplace, but simple lamp timers that are available at all home improvement and hardware stores work well enough for most purposes. I suggest purchasing the heavy-duty (rated 15 amps) timers that offer a grounded receptacle.