Saltwater Aquarium Lighting

Saltwater Aquarium Lighting not only serves to provide visual pleasure and highlight the aquarium, it is also essential to its equilibrium, as fish, like most living beings, need the alternation of day and night, which acts as a biological clock. The action of light also makes it possible for plants to perform photosynthesis and grow.

Marine invertebrates that play host to micro-algae require strong lighting.
An aquarium must therefore be equipped with a light source which resembles as far as possible the one found in their natural habitat, as regards quantity and, most important, chromatic quality.

Quality of The Light
Obviously, the best light would be that of the sun, which permits life on our planet. It is unfortunately impossible to take full advantage of it in an aquarium, for two main reasons.
Firstly, it cannot be quantitatively dosed. This means that too much light often causes the growth of unwanted algae, and so it is important not to directly expose a tank to natural light, especially if it is facing south. On the other hand, if the direct influence is deficient, the aquarium does not receive enough light to ensure that the plants grow satisfactorily.
Secondly, sunlight does not adequately highlight the aquarium and fish. It is therefore essential to resort to artificial lighting placed above the aquarium, usually in a hood specially designed for this purpose.

This lighting must satisfy certain conditions, as regards:
- the type of bulb used and the quality of the light produced;
- the intensity of light supplied to the aquarium;
- the duration of the lighting.
You must be realistic as regards what you can achieve: no artificial light is going to be the same as sunlight. It is, however, possible to get close, ideally with a combination of different complementary light sources.

Intensity of The Light
The total intensity provided by the lighting is an extremely important factor, as plants must be provided the amount of light they need to grow in this artificial environment.
It is inevitable, however, that some light is lost, particularly if the beams have to travel long distances. The importance of the intensity of light (expressed, for the sake of simplicity, in watts) is often under-estimated, and as a result many aquariums are under-lit. It is unusual to find cases of over lighting.
The tables on the following pages give the indications required for obtaining an optimum amount of light for your aquarium.
As a general rule, the use of fluorescent tubes is generally recommended for water up to a height of 0.5 m.

Loss of Light
The further away the light source, the greater the loss in:
- the lighting hood;
- the glass lid covering the aquarium;
- the water.

Part of the light is reflected by the surface of the water, another part is absorbed (the deeper the aquarium, the greater the importance of the absorbed light), and a final part is diffused by suspended sediment. It is estimated that the bed only receives 20-30% of the total light, which can be detrimental to the growth of small plants.
In order to reduce the loss of light, you must:
- recover as much as you can in the hood through reflection;
- keep the aquarium lid spotless;
- make sure that the water is clear;
- maintain the depth of the water below 0.5 m if you are using fluorescent tubes.

Light is important for invertebrates. It must be sufficiently strong to reach the bottom of the aquarium.

Light Sources
A whole host of light sources, each with its own distinguishing features, is available to aquarists.

• Incandescent lamps
These are what we use from day to day in our homes, but they are absolutely out of the question in aquariums: the quality of light is poor, and this type of bulb gives off too much heat.

• Fluorescent tubes
Incorrectly known as neons, these tubes contain a gas that turns fluorescent under the action of an electrical discharge. They give off little heat and are available in various lengths and intensities. They last for 3,000-4,000 hours, or around a year. The quality of the illumination decreases over the course of time, however, and this can be clearly seen if an old tube is replaced by a new one. For this reason, never change all the tubes in a tank at the same time, as plants may be traumatized by this abrupt change in the intensity of the light.

A used tube can be recognized by its black or dark ends. Fluorescent tubes come in various colors: firstly, the cold white or industrial white tubes, which are to be avoided, and the daylight tubes. The latter approximate sunlight the most closely and provide well-balanced lighting. Also available are colored tubes with a variety of dominants, including the tubes with a pink dominant used in horticulture, which are particularly effective for the growth of plants, as they mainly emit blue and red rays, which are trapped by plants and used in the photosynthesis process.

Some aquarists do not appreciate their somewhat unnatural color, which tends to exaggerate the red and blue tones of fish. Sometimes tubes with a blue dominant are combined with white to create a light reminiscent of that found in deep waters. Such tubes are beneficial for corals and other animals from the same group, and have therefore acquired the name of actinia tubes.
Other colors are available, but they are less common. It is sometimes possible to find tubes with a yellow dominant, which are combined with blue tubes to achieve a more balanced light.

A fluorescent tube is not plugged directly into the mains: you must insert a transformer, the ballast, and a starter which produces the electrical discharges required. If you buy a well equipped aquarium, or one with a lighting hood, the tubes will be provided. This does not always mean that you can rest easy, as the intensity of the pre-installed tubes is sometimes insufficient.

• Halogen Lamps
The tungsten filament of incandescent bulbs is here replaced by another metal, which prevents them from turning black. These lamps can be equipped with a rheostat, but they are generally little used by hobbyists.

• Discharge Lamps
An electrical discharge between two electrodes vaporizes a gas, such as mercury or sodium vapor - which emits an intense light. These lamps have a slight yellow dominant, imperceptible to the human eye, which is compensated by a blue fluorescent tube. They heat up and consume more electricity than fluorescent tubes. Some, known as HQI daylight, are prized by aquarists, but they are expensive and impractical for normal tanks. They are mainly used in seawater aquariums over 0.5 m in height, as they help to acclimatize Anthozoans with Zooxanthellae.

• The Hood
Whatever type of light source you choose, it requires a support: this is the hood. Fluorescent tubes must be included in a hood, out of reach of splashed water. It is often protected by a pane of glass but. If this is not the case, the aquarium lid serves the same function. To avoid any loss of light, any partition between the lighting and the water must maintain its shape when exposed to heat, as well as being transparent and. above all, clean. Glass is therefore the ideal material.

Loss of light in the hood can be substantial, sometimes up to 20-30%. There are a few tricks which can resolve this problem, the main principle being to reflect as much light as possible towards the water. You can, therefore, line the inside of the hood with the smoothest possible aluminum foil, coat it with white or metallic paint, or make one or several semicircular metallic reflectors to fit round the tubes.

Some galleries on the market use one of the last two techniques. As the intensity of the light decreases when it gets further away from its source, it is important for the latter to be as close to the water as possible. It should not be any closer than 5-8 cm, for technical and safety reasons, but even with these restrictions the illumination can be satisfactory. (This reduction in intensity has been taken into account in the calculations for the strength of the lighting and the number of fluorescent tubes.)

Good Lighting Requires Good Installation
• The positioning of fluorescent tubes in a hood
The fluorescent tubes must be distributed with, optimally, a distance of 8-10 cm between them (diagram 1). In the fitted aquariums that are commercially available, the length of the tubes matches that of the aquarium, although it is noticeable that the sides of the aquarium receive a little less light than the center or the front and back.

Problems arise when the tubes are markedly shorter than the tank, which can occur in commercial aquariums with unusual dimensions, or in homemade ones. If the tubes are all centered, then there is a space on both sides, which may disadvantage plants on the sides of the tank. A partial solution to this problem is alternating the position of the tubes along the sides (diagram 2).

Another option is the use of tubes of different lengths, making sure that they are arranged to cover the whole surface of the tank and that their total intensity is sufficient.

• How many fluorescent tubes are needed for good illumination?
The number of tubes required depends on their intensity and the size of the aquarium. Here are some indications for water of a maximum depth of 0.5 m:

•These are the data, according to some standard dimensions, for a normally planted tank:

Duration of Lighting
High-quality lighting serves no purpose if it is switched on only for a few hours a day; by contrast, there is no sense in providing illumination for 15 hours a day if the lighting is inappropriate. One will not compensate the other under any circumstances. Once the lighting is suitable, both qualitatively and quantitatively, you must decide for how long you are going to switch it on.

In tropical regions, the day lasts for approximately 11 to 13 hours, and this is what wild plants and fish are accustomed to. The situation is different for plants and animals raised in captivity, which can tolerate different lighting, but always within the bounds of reason. An aquarium can be lit for 13 hours a day, but some hobbyists exceed these limits, as they get used to turning the aquarium on when they get up and switching it off late at night. In this way the lighting can be on for stretches of 16 or 17 hours, which is far too much. It does not especially harm the fish, but it nevertheless changes the balance of the aquarium, and is particularly conducive to the development of algae. It is advisable to keep the lighting on for about 10 hours and switch it off at around 10 or 11 o'clock at night.

The use of programmed electrical clocks facilitates this operation, and particularly avoids any abrupt and unnatural transition from dark to light, which can be harmful to some fish in the aquarium. In this way, the aquarium will receive the light of the new day first, followed by its own lighting. Once the artificial lighting has been switched off at night, the tank will still be able to take advantage of the ambient lighting.

It is also possible to create a program that switches the fluorescent tubes on and off, one after the other, using several timers, thereby recreating, to a certain extent, sunrise and sunset. The ideal lighting program would therefore switch on the room's ambient lighting in the morning, or allow the dawn light to exert its influence, and then turn on one tube about 1 hour later, and finally switch on the other tubes a little later. At night, it would first turn off some of the tubes - with just one remaining lit - then, a short while later, the final tube, and finally, the ambient lighting in the room.

Last but not least: do not interrupt a day-time light. Several hours of darkness, whether total or partial, unbalances the growth of plants and the behavior of fish.