Aquarium Lighting – What Are Your Options?

Water quality (in which I include water movement) is top of the list in importance when it comes to keeping a saltwater aquarium. Closely following water quality is [tag-tec]aquarium lighting[/tag-tec], as much life on the reef depends on it.

The lighting used for a reef aquarium is more intense than on any other type. The reason for this is that we are trying to simulate the sun as far as humanly possible. [tag-tec]Reef aquarium lighting[/tag-tec] is normally more towards the blue end of the colour spectrum as we are trying to produce the lighting colours present at between 10m and 30m in water depth.

Colours are lost the greater the water depth is, the first loss is red. The reason we choose colours present at the depth given is that is the depth where the majority of corals are obtained.

The provision of lighting for a marine reef aquarium needs careful consideration. The depth of the aquarium, distance of the lights from the water, and the type of animals you wish to keep are questions you need to ask yourself.

In the aquarium corals receive energy from the light which is provided for them. The remainder of the energy required is from the corals themselves actively feeding. I will produce a post in the future which will cover various ways to feed your corals.

In the marine reef aquarium the aquarists has a responsibility to supply the light the animals would receive in the wild as far as possible. Obviously we cannot equal the sun itself, particularly its intensity, however we can produce the spectrum of light essentially required.

In the wild the light provision is simple. In basic terms light is provided for around 12 hours a day and a night period of around 12 hours. The light provided by the sun is very intense even when there is cloud cover. The amount of lighting wattage we would need to provide the aquarium to even come close to this sun power would be enormous. In terms of cost and physically fitting the lights it is clearly of no use to an aquarist.

Some people wonder why they purchase a really colourful coral, take it home and over time it loses it colour or its colour dulls. The reason for this is they are used to a certain amount of light, both intensity and colour spectrum. A marine reef aquarist purchases the coral, takes it home and places it in the aquarium and both the light intensity and the spectrum are different to what it is used to or requires. If the lighting is not strong enough or too strong, or of the incorrect spectrum then the coral could lose its colour.

Can’t win! Well, it’s not that bad in reality.

Another thing we could consider producing are ripples on the water surface. There are some aquarists who do not see this as relevant. The way I see it is that it is like this in the wild so we should carefully consider producing these in the aquarium. Ripples on the water surface create a shimmering effect, and there are lots of discussions going on at present as to whether this has any importance to corals. In a reef aquarium, water movement is such that ripples are likely to be produced without any additional effort.

Another aspect is cloud cover – again in the wild the skies are not clear all day long – there are times when there are clouds in the sky. This is something again which you may want to consider when investiating your lighting options. There are lighting models available nowadays which attempt to simulate this.

Another type of lighting which you could consider applying is artificial moonlight. There are various devices available for this. Also there are various theories as to why applying moonlight is of benefit – one of which is coral spawning.

When we consider the power of our lighting, we are thinking in terms of watts. A halide bulb, for example, could be 150 watts, 250 watts, 400 watts etc. As the wattage increases the light is generally more powerful and intense.

Another important point which needs to be discussed is the lighting colour spectrum and the effect which water depth has upon it. While the importance of intensity is well known the colour spectrum is something which must not be ignored.

Light is a combination of different wave lengths which range from the invisible ultra violet, to the blues and yellows etc, on to the infra red light at the other end of the spectrum which again is invisible. These different wave lengths (colours) are rated in Kelvin. It is often referred to as the colour temperature.

The aquarist needs to apply the correct colour temperatures, or Kelvin rating, in the lighting as most corals require this to continue their life functions.

This is where we move on to the next step. Why do corals need lighting, and why is the colour of the light important?

The reason is the zooxanthellae, otherwise known as symbiotic algae, which live within many corals. The zooxanthellae use the light as a source of energy. The coral receives sugars which are the ‘paymentt’ from the zooxanthellae. The zooxanthellae primarily use the blue end of the spectrum. When light hits the water surface red light is the first to be filtered out and so on until, at the depths where many corals exist, generally speaking blue is prevalent.

It must be pointed out that the foregoing is a very simplified version of a complicated subject.

Lucky for the aquarist that light colours are lost as water depth increases. As said, we cannot generate the power of the sun. We can generate enough power for our needs, and the colours of light required by our corals.

When discussing marine lighting, “blue (actinic)” often crops up. This is light, mainly generated by fluorescent tubes, which is used both on a full fluorescent lighting system, and also on a halide system. This blue light is used for the reasons already discussed.

So there we go, in vary basic terms the above covers the importance of lighting and the effects that water has on light but this still leaves the questions :

How can we create this lighting in the home aquarium?

The best thing, in my opinion, is to ask yourself:

“What animals am I hoping to keep?”

The answer to this question will determine the type of lighting you will require.

The choice of lighting for use in the aquarium depends upon various factors:

  1. What corals are to be kept in the aquarium
  2. The depth of the aquarium
  3. Cost

There are at present two main types of lighting which are used for the aquarium:

  1. Fluorescent Tubes
  2. Metal Halides

Fluorescent tube lighting comes in quite a few colour types as well as power and size. The good thing about fluorescent lights is that they are quite cheap to run, produce little heat and are relatively cheap to purchase. It is important that these bulbs are replaced at the latest annually otherwise the light output is seriously altered.

Fluorescent tube lighting does not penetrate the aquarium water as well as halide lighting does. When fluorescent tubes are used, light needing soft corals can be kept down to around a maximum depth of 35 cm (13 3/4″), and light needing hard corals can be kept down to a depth of 10-12 cm (4″ to 4 3/4″). This seems a precise ‘rule’, but is intended as a very general guideline.

Fluorescent tubes are a good purchase if you have a shallow tank and/or are looking to keep soft corals. Fluorescent tubes normally do not have the output to sustain short polyp stony (SPS) corals unless the corals are at the very top of the aquarium. With SPS corals it is best to opt for the more powerful halide lights (alongside two blue (actinic) tubes). If you do decide to use fluorescent tubes for your lighting then ensure that reflectors are fitted to direct the maximum amount of light to the aquarium.

When fluorescent tubes are fitted as the lighting system for a reef, fit as many tubes as is practical for the space from front to back, with the tubes running the length of the tank, and allowing the use of a reflector for each tube. It is best to have the same number of marine white tubes as blue (actinic) tubes. If an equal number will not fit, make the odd tube a white one. Remember, however, that fitting extra tubes does not increase light penetration. It spreads the light and more of the area of the tank will receive it. Introduce a ‘dawn and dusk’ cycle by using electric timers. Set the white tubes to be on for between 10 and 12 hours a day. Set the blue tubes to come on 1/2 hour before and switch off 1/2 hour after the white. The fish will appreciate the increase/reduction in light.

One thing that must be noted is that it is poor management to plunge an aquarium into darkness or suddenly bathe it in light.

Currently, the best type of tube to obtain is called a T5. Earlier tubes come under the name T8. The ‘5’ and ‘8’ refer to the diameter of the tube, the 5 obviously being smaller. The ballasts for T5 tubes must be electronic. A single electronic ballast can be obtained to drive two T5 tubes, thus saving space. In my opinion if you do not wish to, or do not have the requirement to implement metal halide lighting then [tag-tec]t5 aquarium lighting[/tag-tec] is a very good investment.

There are other tubes called very high output tubes which, true to their name, push out more light than standard fluorescents (about 3 times as much light). Like all electrical items they do generate heat, more than standard fluorescent tubes but nowhere near as much as metal halides. If heat is an issue, if you are using a light canopy, or do not like the idea of a metal halide pendant then VHO fluorescent tubes may be a good choice for you. VHO tubes will give you the ability to keep some of the SPS corals, and all of the soft and LPS corals.

Metal halides come in a variety of sizes, power output, bulb type and Kelvin variations. When using a metal halide it is important that ultra violet shielding is provided. This can be either by using special protective ultra violet shielding glass built into the metal halide unit, or by using an ultra violet shielded bulb.

Metal halides have high power output, much more so than fluorescent tubing, and have the ability to penetrate even the deepest of aquariums. In the following table, the ‘K’ in the first column stands for Kelvin, which has been discussed earlier. Also note that 2.5 cm = 1 inch (not absolutely accurate but near enough).

Halide Max Soft Coral Penetration Max Hard Coral Penetration150W @ 10,000K 51cm 22cm
150W @ 20,000K 56cm 27cm
250W @ 10,000K 61cm 35cm
250W @ 20,000K 68cm 38cm
400W @ 10,000K 74cm 51cm
400W @ 20,000K 79cm 56cm

When keeping a coral reef aquarium, particularly where hard corals are concerned, the best choice in my opinion is metal halide, therefore for the remainder of this post I am going to concentrate on these. This does not necessarily mean that a metal halide is the best choice for you, standard or VHO fluorescent tubes may be a better requirement dependant upon your needs.

Though it is not an absolute requirement, many aquarists run two fluorescent blue (actinic) tubes with the halide(s) and this is recommended. This not only increases the important blue light, but allows the introduction of a ‘dawn and dusk’ cycle using electric timers. Run the halide(s) for 10 to 12 hours a day, and set the blue tubes to come on 1/2 hour before and go out 1/2 hour after the halides. The fish will appreciate the light progression in both directions. Sudden bathing of a tank with light or plunging it into darkness as said is bad practice.

When positioning a metal halide unit over the aquarium it is important to position it strictly in accordance with the manufacturer’s instructions. The units are considerably higher above the aquarium than fluorescent tubes need to be. This is because they run hot and any water splashes could be dangerous, even cracking glass. Remember to let them cool down before cleaning any dust etc from them.

Metal halides normally consist of three components, these being the bulb, the ballast and the reflector. A metal halide unit can be purchased complete where all the components are built in, alternatively they can be purchased separately.

Let’s go through each of the components in further detail as it is important to understand each one.

Firstly we’ll discuss the bulb.

The bulb is the part of the metal halide unit which provides the light. The choice of lamp depends upon the corals you are going to keep and the depth of the aquarium. The choice of bulb ranges in power from 150W all the way through to 1000W and Kelvin ranges from 6500 to 50,000. It is recommended that metal halide bulbs, as with fluorescent tubes, are replaced to prevent loss of light quality. The replacement of a metal halide bulb is recommended every 12 months.

The normal Kelvin rated bulb used in an aquarium is between 10,000 and 12,000 Kelvin.

Two things to remember though when it comes to the metal halide bulb:

  1. The higher the wattage the deeper into the water the light will travel
  2. The higher the Kelvin the more blue it will appear

There are of course other things to remember. First, you need to ensure that the correct amount of both wattage and colour is provided to ensure the health and growth of the corals. Second, the lighting provided needs to be pleasing to your eye. Applying some high wattage lower Kelvin lighting (halide), say 10000K, to the aquarium and then supplementing this with lower wattage but high Kelvin lighting (fluorescent) gives a visually pleasing light as well as providing the corals with what they require. Normally the additional higher Kelvin lighting is provided by using blue (actinic) flluorescent tubes. This also opens the door to a ‘dusk and dawn’ sequence using electric timers.

Let’s move on to the reflector which is another important part of the metal halide.

When lighting your aquarium by metal halide you need to get as much of the light produced into the aquarium as possible, and not into the hood, room etc. This is why an efficient reflector needs to be used.

The bulb obviously emits light from all areas including upwards. If a badly designed reflector were used then the light could be reflected over an area wider than the water surface, wasting light.

A correctly designed reflector on the other hand will reflect the light from the bulb into the aquarium with minimum if any overspill.

If you are purchasing an all in one unit then you will have everything required. If you are considering using individual components then you will have your choice of reflectors to choose from.

The ballast is the component of the metal halide which ‘fires’ the bulb and then regulates the voltage so that the bulb can run correctly.

There are two types of ballast units available, these are magnetic and electronic.

The magnetic ballast is normally a lot heavier than its counter part and makes quite a loud noise when starting the bulb.

An electronic ballast, on the other hand, is smaller, a lot quieter and in general produces less heat.

So now we have been through what makes up a metal halide unit. The decision you need to make is whether you should use an all in one unit or purchase separate parts.

This really is up to you. There are some very pleasing to the eye all in one pendant based units available which provide everything you need.

I prefer to use metal halides built from separate units as I can meet my exact requirements. The ballast can be hidden from view and the reflectors hidden in the hood of the aquarium. If using the hood as an enclosure for halide lights, there must be adequate ventillation. Many aquarists run fans to extract the heated air, the same type that is used on computers is one option.

Editors note : What I hoped to be a short post about lighting suddenly turned out to be quite a large one, but then it is a rather large subject area. I would be very interested in your opinions in relation to lighting – if you would like to express your opinions on this really interesting subject then you can do so in the comments section below – I look forward to hearing from you.

Aquarium Lighting – What Are Your Options?
Rate this post
1 Comment
  1. I need advise –
    I have a tank that is 80″ wide by 18″ deep and 30″ tall am I going to have a problem making this a reef tank because of the 30″ in height> If not, what kind of lighting and how much do you reccommend?

    Thank you,
    Chuck Kraus

Leave a Reply