Table of Content

Lighting and Spectrum
Lighting and Temperature Control
UV Protection, and Bleaching
Lighting and Algaes
Moonlight Option
Choosing Your Own Lighting Systems

Lighting and Spectrum

We say that a lighting system is the other most important equipment besides a protein skimmer in keeping a successful tank. The rule of judging whether a lighting system is good or not is to check if it provides the desired spectrum for the corals in the tank. A good lighting system is a-must in any reef tank since corals are very sensitive to the spectrum.

To understand why a lighting system is so critical, we need a bit of understanding of the "spectrum" that we constantly refer to. As you know, visibile light consists of different components (colors). The difference among all these colors is that each color has a unique frequency of Electromagnetic (EM) oscillation. A better way to put this is that light is really an electromagnetic oscillation. The visible light spectrum, from red to purple, is only part of the very big electromagnetic oscillating phemonena. What is so special about each of the different lights is its unique wavelength of which each "color" oscillates. In Physics, each different types of EM oscillation is also identified by saying the frequency of which the oscillation occurs. Since there are many different types of oscillations and each has a unique freqeuncy associated with it, when we put all the oscillations together on a common axis, the common axis becomes the frequency spectrum. (Note that wavelength is the reciproal of frequency. Hence the longer the wavelength, the lower the frequency.)

The keys to realize when you choose your lighting system is that each EM wave penetrates water differently. Hence, depending on the type of corals you want to keep in the tank, you will have a different lighting requirement for each of them. As you know, energy is carried by light. (Remember your last Sun-burn?) Hence, the penetration of the lights means the amount of energy that can reach different levels of your tank. It simply means how much energy (light) can reach the bottom of the tank? Since some corals require more light than the others, it is necessaary to ask your dealer about that. Because of this penetration issue, you can see why we always recommend to our customers not to have a tank that is too deep. A deep tank poses a tight requirement on the lighting system. If the lighting system is not suitable, nothing can live beyond a certin level of the tank. There are also a number of books that give you a good guideline for the different requirements, such as lighting, pH level, of different species. These are very good books for quick reference and for learning more specfic requirements, you may consider keeping one of them in your saltwater aquarium library.

Lighting and Temperature Control

In the usual setup, the lighting system is hanging on top of your tank. Hence, your lights are also the biggest source of heat in your tank. Since the water temperature should always be maintained in the range of 23 to 27 oC, you need to consider the temperature issue quite seriously. Corals like the lights, but they dislike the heat. In maintaining a roughly constant water temperature in the tank, we rely on a good circulation system that distributes the heat evenly in the tank and adding water to the sump regularly. A circulation system prevents the extreme temperature near the surface. Adding water to the sump is to replace the water that has evaporated due to the heating near the surface.

Temperature sensor is a little piece of electronics that commonly used to measure the water temperature. (Other temperature measuring devices are also suitable.) What the temperature sensor can do for you, however, is more than only measuring the temperature. As we just mentioned about the heating issue, there is really no way you can determine the number of hours you should keep lights on. We usually recommend 10 hours of operating time for the lights, but the number depends on the tank size, circulation, how much heat is carried away by the evaporation. The best way to figure the number for your own tank is to run a series of experiment on your own.

Before you run your experiments, first, mark down the number of hours you keep your lights on and the water temperature. Keep these numbers as your reference. Consult with the books that we said in the spectrum section for the best suitable temperature range for the corals that you have in your tnak. (Since it is your tank, this is your call.) If you are interested in a particular type of soft corals, look it up in the book and find out the requirements. For a week or so, keep track of the number of hours the light is on and the water temperature your sensor gives you. Then start changing the variables to determine what is the best thing to do in your tank. This little experiment can be very useful when you are upgrading your system and you have no idea of how much heat is generated by the lights and all the impacts that we talked about earlier.

Please remember that the 10 hours rule-of-thumb should be treated as the initial guess only. To find out what is happening in your tank, you need to run this experiment. Yes, this requires work and it is the committment issue we were talking about on FAQ III.

UV Protection, and Bleaching

UV light has wavelength just below the violet radiation. UV light is a common topic that our customers usually ask. Some people are excited about UV protection. Some people are confused with actinic blue lights and the "UV lights". The first thing we always remember is that there are 3 types of UV light, UV-A, UV-B, and UV-C. UV-C is used in the UV sterilizers to get rid of planktonic fish parasities. Since UV-C kills any living tissues, bacteria and floating micro algaes are also killed in the sterilizier. If you are using a sterilizier, check if the temperature is about 40oC. Because of the nature, UV-C is never used in the tank and the blue light that you see above a tank is actinic light, not UV-light. In fact, we will be blind if our eyes come into contact with UV-C light.

Although it poses less damage on living tissues than UV-C, an excess dose of UV-B is also harmful. The beneficial UV-light is UV-A and should be provided by your lighting system to the corals. It is particularly important to autotrophic organisms. If you remember from More Bio Filteration page, we mentioned that there are 2 ways to categorize bacteria. One way to do it is to group bacteria according to how they generate energy to support their only living. If the bacteria gain the energy by consuming the glucose, they are heterotrophic. On the other hand, bacteria that can generate energy for their needs without consuming glucose are autotrophic. For example, nitrifying bacteria gain the energy by oxdiating inorganics (not by consuming glucose), hence they are autotrophic.

The significance of UV light is that first, your system must not be emitting UV-C wave. This is usually a concern with metal halide light since the intensity of the light is extremely high. If you are using a metal halide light, it is necessary to have some kind of filter lens that filters the UV-C before the light radiates to the tank. On the other hand, if the lighting system provides too much energy, it leads to bleaching of the corals. Bleaching of your corals is the same as Sun-burn to human. Bleaching is one of the few common ways of losing your corals since the corals are so close the the light source, or the "Sun".

Generally speaking, an abnormally high temperature and a high UV-radiation are closely rrelated with the coral bleaching. Let us briefly look at how corals protect themselves from excess radiation. In order to protect the corals from the excess UV-radiation, there is a certain amount of the active forms of oxygen molecules in the water that block the harmful UV-light. This is really the same idea as having our atmosphere to protect ourselves from the excess UV-radiation from the Sun. High temperature level provides the living conditions for some types of hormones that can break down these oxygen molecules. When the hormones begin to break down the active oxygen molecules, there are less active oxygen molecules to protect the corals from the UV-radiation. The excess UV-light kills off the pigmentation tissues in the corals and the corals in the water appear pale. Losing the pigmentation tissues is the same as to have no protection against the harmful UV-radiation and this kills the corals. Since there is no easy way to measure the intensity of the the light shining from your light, rather than going into the very expensive equipments, to monitor the water termperature, use water temperaure as an indicator instead. As a general rule, the water temperature should be between 23 to 27 oC.

lighting and Algaes

Algaes are always present in your tank; they are plants that live in the water. Same as corals, algaes are capable of doing photosynthesis. Algaes convert inorganic material, water, and carbon dioxide molecules into sugar in the form of glucose. There are generally 2 stages in photosynthesis - the light reaction and the dark reaction. Obviously, it is the light reaction that your lighting system plays a role in the whole process. Inside the living cells of the corals, there are different types of pigments. These pigments are capable of absorbing energy at different frequencies. Same as other plants, algaes are capable of doing photosynthesis. In fact, it is the most dominating pigment that gives the color of the coral.

However, as you know that not all algaes are welcomed in the tanks. This is paricularly true with the green algae. Green algae can usually be found under the bases of corals. They are bad because they weaken the skeleton of the stony corals, and hence, the bases become soft. This eventually destroys the bases and kills the corals. There is another reason for which we want to keep the growth of algaes under control. We said that algaes are capable of doing photosynthesis and they convert inorganics into organics. The problem comes in when the algaes decay. The inorganics that were stored inside the algaes' cells will be released upon the death of the algaes. For this reason, algaes are also known as the "nutrient bombs". When the "nutrient bombs" explode, they release excess amount of nitrogenous compounds into the tank. Unlike the ocean, there is comparatively much weaker current and a much smaller volume in the tanks.

Realistically, green algaes bother every tank once in a while: The tank was doing fine until the last week or so. There is nothing wrong from your chemical tests. This may be a hint for you to change your light bulbs. There is a certain amount of Argon and other gaseous chemicals inside a new bulb. Firing up your lights 10 hours a day is going to cost you some of the Argon gas. Slowly the Argon gas inside the bulb will be used up as it approaches to its end of the bulb's life expectance. If the bulb has passed its life expectance and it is still in use, the bulb will not give the correct spectrum, and hence, you will find the green algaes growing a lot faster then it normally does. If the algae problem is bothering you and every chemical test shows perfect result, try to change your bulb. When you purchase your bulb, ask your dealer when should you expect to change your bulb so that you have a better idea of what to expect.

Moonlight Option

Recently, many of our customers have shown their interest in the moonlightlight option. The common question is that they are interested in installing one, but wonder if they need to replace the whole system to include a moonlight option.

Why moonlight? The moonlight system is designed for the nocturnal corals and inhibitants. It provides the suitable lighting intensity for these nocturnal corals and inhibitants at the times when they are naturally active in the ocean. The nocturnal corals and inhibitants are organisms such as zooplankton. When the lights are off, zooplankton, become much more active than in the "day" time. (The "day" time is the time when your lights are on.) Invertebrates like shrimps and crabs, or corals like sun polyps will be actively looking for these zooplankton after the lights are gone. (Plankton is a family of organisms that float in the aquarium and simply follow the stream of the current in the tank. Brime Shrimp is also a member of the Plankton family.) If you are feeding Brime Shrimp to your fish or to your corals, the moonlight system is an important equipment for your tank.

For those of you who like to try the moonlight option, it is not necessary to change the whole system. There is single moonlight unit available. The one that we would recommend is aquamoonlight from Aqua Medic. Besides the nocturnal creatures, moonlight reduces stress on the creatures inside the tank in general. In theory, there should be light 24 hours a day, just to simulate the real ocean. Furthermore, reproduction is strongly related to the available moonlight in the tank. Hence, a moonlight unit is more than another fancy toy in the tank. The aquamoonlight from Aqua Medic is a 15 Watt incandescent light. There are 2 special LED's in the unit. The whole unit is only 4.6" * 3.4 " * 2.8 ". It can be added on to the existing system easily.


One thing that we have not talked about so far about using your lights is to establish a light cycle. Basically when you switch on and off your lights between certain hours a day, you are establishing a light cycle. However, switching the lights on and off suddenly creates stress and even shock. Therefore, a better cycle is to simulate the real Sun-rise and Sun-set instead of switching on and off suddenly. The way to do this in a tank is to gradually switch on the lights in the morning and slowly dim off the lights at night. To do this automatically and accurately requires the use of a timer. With a timer, your actinic lights may be switched on a couple of hours before the metal halide lights is on. Similarly, the timer can be set so that the metal halide light is off a coule of hours before the actinic lights. If you are using a moonlight unit, you may also choose to establish a moonlight cycle to maximize the benefit of your moonlight unit as well. To establish a moonlight cycle really means helping your corals and micro-organisms to reproduce. The general idea is to establish a moonlight cycle that has a period of 29 days. The moonlight intensity should be increased gradually from the minimal level to the maximal in the middle of the period, then back to the minimal level at the end of the period. However, to establish such a moonlight cycle is not easy if it is done manually. Please check with your dealer about this if you are interested in the details.

Choosing Your Own Lights

There are many lighting systems available in the market. However, this discussion only looks at the most popular ones. As we mentioned above of all the signuificant reasons of getting a nice lighting system, another big factor in choosing your lighting systems is prices. High quality lights are good in providing the spectrum for the corals and low in maintainance. But they are expensive. Low quality lights, on the other hand, are more for beginers and they calls for maintainance frequently.

There are generally 4 different types of lighting systems available in the market at this moment. The most obvious one is light bulbs, usually in the dual - lighting setups. The next level lighting system is Power Compact systems, such as Phase II and Phase IV from Red Sea. Beyond the Power Compact systems are the advance systems, such as aquastarlight and aquaspacelight. These advance systems come with a metal halide lights and actinic blue options. Moonlight options are usually available for these systems as well.

Light Bulbs and Installing Your Own Lighting Systems

Light bulbs are the perfect choice for the beginers in saltwater aquariums because they are simple to understand and relatively inexpensive. A typical setup has a so-called dual set light bulbs. That is, a day light and an actinic blue light. Basically, these 2 are all you need for keeping a saltwater aquarium. In addition to the basic set up, it is very common to include a reflector so that the amount of lights going into the tank is maximized.

Dual Light Strip

On the far left, we have a picture of a Dual Light Strip from CORALIFE. It is the best lighting system that you can get if you prefer the flourescent lighting system to another popular system - Power Compact system. The unit that is shown here has a Mirror Reflector, a BJB Water Proof End Cap, and an Electric Ballast. The Electric Ballast is the same as the one that we have shown on the More Lighting System when the we discuss the DIY option of your own lights.

However, this system does not come with any light bulbs. You will need to buy them separately. Usually, we do recommend our customers to go with the CORALIFE ACTINIC 03 Blue and the CORALIFE 50/50 (50 % Natural Daylight 6000K and 50 % Actinic 03 Blue) If you are running your lights 10 hours a day, then you will need to replace them every 6 months.

On the left is a picture of the CORALIFE ACTINIC (the rightmost) and 50/50 (next to the ACTINIC). For this particular series of products, both the 36 and 48 inches long lights are commonly available.

Installing Your Own Lighting Systems

The Dual Light Strips is only an option for beginers. If you are interested in installing your own system, here is a piece of equipment very handy for you. This set of electronic ballast is from Coralife and it is a very popular item for poeple who like to do their own work. If you are interested in getting a Moonlight system also, you can also purchase Aquamoonlight unit and a timer separatedly to make a wonderful and inexpensive system.

The ballast included in this setup is identical to the Dual Light Strip. However, a reflector is not included in this package and can be purchased separated if you need one.