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Reef Lighting

Coral in Saltwater Aquarium

lighting your reef

Proper lighting for reef aquariums is another one of those hotly debated topics in the hobby. There are many opinions and really no one correct way or perfect lighting system for your aquarium. However, there are many options and all these options can make the beginner or even advanced reef keeper confused. Proper lighting is essential to the long-term health and vitality of your reef aquarium because most animals you wish to keep have some photosynthetic component and depend upon proper lighting for their nutritional needs. Hopefully the following introduction will help you to decide on the best lighting for your reef aquarium or at least lead you into a direction to find more detailed information.

Seek Advice

Lighting is one of the most expensive components of your system and I highly recommend that you ask lots of questions of other reef keepers in your area about their lighting and their honest opinions, a reef keeping club in your area is an excellent source for this information. Be aware that for every fellow hobbyist you ask you may get a different answer as to the best lighting. Slowly sift through all their advice and look at their tanks for an idea of how the lighting will look on your tank. Short of going to many hobbyist’ s homes and personally seeing their tanks, you can visit some of the online reef keeping bulletin boards and check out the Tank of The Month feature. These tanks are some of the finest in the world and have in depth descriptions of the lighting systems used. You may quickly find yourself confused because for every type of lighting there are those that love it and those that hate it. It's just like salt mixes, there is no best, all have their pros and cons.

Basic Types of Lighting

There are three basic types of lighting used for reef aquariums, fluorescent lights, metal halide lights, and LEDs. LED lighting is a great new option introduced just a few years ago and has revolutionized reefkeeping. 

Fluorescent lamps are long and produce a more spread out even-looking lighting. Metal halide lamps will produce a more point source spot type lighting that simulates the glitter lines as when sunlight shines through water. LEDs are unique and usually fixtures contain many individual bulbs.

Spectrum -The Color of Light

Corals look best and grow best under light with a more blue coloration, in my experience, and that of many successful reef aquarists. So, I advise having more blue spectrum lamps on your reef aquarium. Most corals we keep in our aquariums originate in the wild from deeper water and therefore most yellow and red light is filtered out leaving blue.

Light color that a lamp produces is measured in degrees Kelvin, abbreviated K. Kelvin ratings do not relate to light intensity directly, a higher K number does not represent more intensity, in other words a 20,000K lamp is not more intense than a 10,000K lamp. This is something that a lot of folks get confused about, I will get calls all the time from folks that say they just added more intense 20,000K lamps to their tank. Wrong, they added more blue light to their tank with the 20,000K lamp and not more intensity.

Lamps for aquariums will have K ratings listed on them and this relates to the color temperature, the lower the K number the more yellow-red the light will be from that lamp and the higher the number the bluer the color of the light from that lamp. For example, a 6500K lamp will be very yellow in comparison to a 20,000K lamp that is very blue. Intensity tends to decrease as the K rating increases. So, a 6500K lamp will produce more light than a 10,000K lamp and it will produce more light than a 20,000K lamp at the same wattage.

Wattage— How Much Light Do You Need?

As with the type of lighting and the best color spectrum to use, the optimum intensity is also debated in the reef keeping community and there are no firmly set guidelines for the beginner to adopt. Again, if you ask many successful hobbyists you will get many different answers about how much light is needed to grow corals. A lot depends upon what type of corals you wish to keep. While the corals we keep in our aquariums all originate from tropical waters and are used to intense sunlight, some are more adaptable than others to captive life and changes in light intensity.

Acropora corals and other smaller polyp stony (SPS) corals are less adaptable to varying lighting conditions than larger polyp stony (LPS) corals and soft corals. Often folks will keep soft corals and some LPS corals very healthy and growing well under just regular fluorescent lamps or power compact fluorescent lamps and SPS corals under a combination of metal halide and fluorescent lamps.

The wattage of the lamps and type of ballast used to run the lamps will determine the intensity of the light the lamps produce. Over the years hobbyists have discussed crude measurements of the amount of light corals need to thrive. Most successful reef aquarists will use about 6-8 watts of light per gallon of tank water, more in deeper tanks and less in shallower tanks. There are others such as myself that grow corals successfully in a greenhouse with just natural sunlight or even in an aquarium illuminated with skylights or solar tubes or a combination of sunlight and artificial light. With higher light levels on your tank you will be able to successfully keep a wider variety of corals than with lower wattage. If you have only regular output fluorescent lamps you will only be able to keep a few corals alive, but if you have metal halide lamps in combination with fluorescent lamps you will be able to keep almost all corals healthy and thriving.

With the now widespread use of LED lights the discussion above about wattage is somewhat obsolete. Although many hobbyists still use some type of fluorescent lamps and metal halide and are very successful using them. Use of some type of waterproof meter to measure light intensity is much more reliable, such as the use of a par meter.

Expense is often the limiting factor in how much light can be used on an aquarium. Higher grade fluorescent and metal halide lighting can be quite expensive and the associated heating of the water with higher wattages will demand expensive temperature controllers and chillers to be employed. LED lights are very popular because they do not produce much heat, provide excellent light intensity and color, and can be controlled remotely in many ways that other types of light can not be controlled.

Types of Lighting

Flourescent Bulbs


Low Output (N.O.)

These lamps are the same as you find in home and business ceiling lighting fixtures. For aquariums they are usually sold with freshwater of saltwater fish-only tank set ups often coming as a package with a tank, glass top, and strip light. In a smaller aquarium of maybe 30 gallons or less they can be used to keep some corals successfully. Low light demanding corals such as mushrooms and some Zoanthids may do well with this type of lighting. Other lower light demanding corals may be OK if you have several lamps over the tank. This type of lighting would be considered the lowest intensity usable for a reef aquarium. If you are on a tight budget you can keep some corals and also fish and invertebrates in a reef aquarium illuminated with N.O. fluorescent. This lighting would not be appropriate for any corals that have higher light demand.

Power Compact

Power Compacts (PC)

This type of fluorescent lighting is commonly available at a relatively inexpensive cost. Many hobbyists choose this type of lighting and at one time was the most commonly used lighting for reef aquariums, but has now been replaced with LEDs. I would also consider this type of lighting of lower intensity. You can successfully keep a reef aquarium with these lamps, but as with the N.O. fluorescents I would suggest only soft corals and some LPS corals. If you have several lamps over a smaller tank then this type of lighting would be OK for many varieties of soft and LPS corals, it would not be appropriate for most SPS corals.

T5 Lighting

T5 Lighting

High Output (H.O.) (V.H.O)

High output lamps (H.O.) and very high output lamps (V.H.O) will allow you to keep most corals thriving if you use enough of them over your aquarium. They are now commonly called T-5 lamps. Again, using a combination of lamps to get a bluer color will make your corals look their best. Some hobbyists are quite successful keeping even the more difficult to keep SPS corals including many Acropora with T-5 lamps. These lamps are thin and many can be included in a homemade type canopy and they are now readily available in retro fit kits. They also have an advantage over many other types of more intense lighting used for SPS corals in that they will not heat the water as much as high wattage metal halides. As with other fluorescent lamps these should also be changed about every 6 months because over time the intensity and spectrum of the lamps change and if you wait too long you can shock your orals and cause them to bleach or die.  

Metal Halide Lighting

Metal Halide

There are two types of metal halide (MH) lamps, single ended screw-in, also called Mogul base, and double-ended lamps called HQI. Metal halide lamps have a smaller tube section enclosed by a larger glass envelope, the HQI lamps are basically just the inner section without the larger outer envelope. HQI lamps require a different type of fixture than the screw in lamps. The outer glass envelope on a screw-in lamp provides some UV protection and since the HQI lamp does not have this outer glass envelope it must be housed in a fixture with UV absorbing glass. Because HQI lamps are smaller, the fixtures used for them are smaller and sleeker and now many types of unique HQI fixtures are available. Screw-in type lamps can be housed in full metal hoods or pendants and also are available in retro fit kits for installation into your own canopy.

MH lamps produce intense point source light that is especially good for SPS type corals as well as other corals. They do produce lots of heat and thus temperature control will be an important consideration when using these lamps. If cost and temperature control are not an issue and if you can afford to change the lamps at least every 6-8 months then MH lighting is the one type of lighting that has been used for many years successfully and most simulates natural sunlight. 

LED Metal Halide and T5 Lighting


Metal Halide/LED or T-5 Combo

HQI MH lamps are available in 150 and 250 watts and screw-in MH lamps are available in 175, 250, 400, and 1000 watts. For Acropora and brighter colored SPS corals 250, 400, and 1000 watt lamps are the most commonly used, 250 watt HQI lamps also work well. Kelvin ratings typically used for reef aquariums range from the very yellow 6500K up to 20,000K blue lamps. Also available are 10,000K and so-called 14,000K and 15,000K lamps, although these designations are often mostly manufacturer marketing than real distinct values. Each manufacturer’ s lamp will vary in color, one 10,000K lamp may be more yellow than one from another manufacturer yet both will be labeled as 10,000K. So, the Kelvin ratings on MH lamps are not precise and do vary.

For many years I used and recommended 20,000K lamps along with VHO or T5 actinic fluorescent. Typically, the actinic lamps will be on for one to two hours before and after the MH lamps simulating dawn and dusk. Most hobbyists will use the MH lamps for about 6-8 hours a day simulating the height of intensity of tropical sunlight.

Some folks that used LED lighting are now going back to these combination fixtures that use MH lighting. Again, if you can control the heat generated and can afford the fixtures and bulbs then this is some of the best possible lighting.



Reflectors used for your lights are critically important in getting the optimum utilization of the light produced from any type of lamp. Parabolic shaped shiny metallic reflectors are generally better at getting more light into your aquarium than any other type of reflector materials.

Also, the lamps and reflectors must be cleaned frequently with a damp cloth to remove salt spray and dust to get the most out of each lamp. Generally, fixtures should be about 8-10 inches above the water surface to get maximum utilization and lamps should be protected from water slashes that will cause hot lamps like metal halides to crack or sometimes explode. A cracked lamp will emit excessive UV radiation and can easily bleach and kill many corals quickly, so it is advisable to clean and check all lamps at least weekly. Fluorescent lamps should be replaced every 6 months and metal halide lamps generally should be changed about every 12 months. The lamps will produce light for a much longer period but the spectrum and intensity shift and decrease slowly over time. Corals will become slowly adjusted to these lamp changes over time and if you then change a lamp suddenly the corals will be subjected to much more intense light and will be adversely affected. Keeping with a strict schedule of lamp changes will prevent this problem.

led lighting

LEDs (light emitting diodes) are becoming the standard type of lighting for all aquariums including reefs. The benefits include very low electric usage, very low heat generation, extremely long bulb life, and exceptional coral coloration especially zoanthids, Acans, and many other corals look amazing with LEDs. 

Virtually every day new LED strips or fixtures are being introduced so you will need to do some searching online to find out what is currently available. We have used LED lighting and love it and feel this type of lighting has and will continue to revolutionize how we light our tanks. Some fixtures offer unlimited control features from remote locations via your phone. These fixtures can be very expensive. More basic fixtures that have built-in timers and no other programming options are very affordable. As with any lighting option, ask around and look at actual results before making your decision as to what lighting will be best for your tank. Generally speaking, LEDs are the best all around lights for most reef aquariums.


There are many types of lamps you can use for your reef aquarium. Because the lighting is so important to the health of the animals in your care and because of the expense of most lighting equipment, it is advisable to seek as much information and advice as possible before deciding upon the best lighting for your tank. SPS corals require the most lighting while soft and LPS corals can do well even with lower intensity fluorescent lighting. Actinic or more blue lighting should be used even with metal halide lighting to achieve the best possible coral coloration. When using MH lighting some means to temperature regulation of the tank water will be needed so as to not overheat the water. Stability of a constant temperature is critical to the long-term health of your corals and other reef aquarium inhabitants.

LED lighting is a relatively new type of lighting used for reef aquariums with the best overall possibilities.

All lamps need to be kept clean and replaced on a set schedule to prevent adverse reactions and to maximize coloration.