A successful aquarium includes the right lighting system. Aquarium lighting can be as important to the health of the fish as the filtration system, and in some cases such as reef aquaria, the lighting system may be more important than the filtration. This means matching the correct lamps to the type of aquarium you are setting up.

Basic Terms To begin:

You should become familiar with the following terms:

Color number, more correctly called color temperature, refers to the absolute temperature, in degrees Kelvin, of the light produced. This measure is important when trying to simulate the color of natural sunlight, which is about 5,000° K.

Lumens is a measure of light intensity. It is defined as the radiant energy from the visible portion of the light spectrum hitting a given area (for example, in meters or feet squared) when the distance from the area to the light source is equal to the unit of area measurement.

Lux is a measure of the illumination from all light sources hitting a surface from a distance of one meter. It is equal to lumens per square meter.

Full spectrum light is a light source that emits all the wavelengths of the visible spectrum in proportion to that of natural sunlight. A lamp or bulb labeled “full spectrum” emits light over the entire visible spectrum with a spectral output similar to that of the sun.

Intensity is related to the electrical consumption in watts of the lamp or bulb and is measured in lumens. The more watts a lamp requires, the greater the light intensity. Most books on aquarium lighting give formulas or guides for determining the total wattage required for an aquarium. In some cases, this requires a large number of lamps. If lamps of higher wattage are substituted, the number of lamps can be reduced without sacrificing wattage.

Wavelength is an important term, especially in the context of lamp descriptions such as full spectrum or peak wavelength. These terms refer to the wavelength output of the lamp or bulb. Actinic lights, for example, produce light only at a specific wavelength – 420 nanometers. This peak wavelength value, which produces a very blue light, was chosen because chlorophyll absorbs light near this wavelength during photosynthesis. To promote photosynthesis in reef coral, actinic lamps are used. Some lamps have two, or even three, peak wavelengths.

Types of Lights Once you know the above terms, you can better understand the different types of lighting systems. Standard incandescent light bulbs can be used for lighting an aquarium, but are not recommended. They are inefficient, generally poor quality light and produce a great deal of heat.

Fluorescent lamps are manufactured in several sizes such as T-12, T-8 and T-5. The numeric reference relates to the diameter of the lamp. As the industry progresses we find greater emphasis in the use of the T-5 bulb with tighter compression of the phosphor providing greater light intensity. High Output (HO) lamps are available for those who demand even higher intensity for deep water aquaria.

Compact fluorescent bulbs are the next step for intensity. Operating in the same fashion as regular fluorescent bulbs they typically produce up to three times the intensity as a conventional fluorescent bulb of the same wattage. Ideal for both fresh and saltwater aquarium use, equally suitable for growing live aquatic plants.

Metal Halide lamps can be used in reef aquariums. They produce an intense light and have various color temperatures. Metal halide work well but are less efficient than fluorescent lamps, they emit high heat (requiring a fan to displace heat from the aquarium and hood) and generally are quite expensive.

LED or Light Emitting Diode lighting is relatively new to the aquarium industry. Although the technology of running current through a two-element electron tube or semiconductor through which current can pass in only one direction has been around for decades, refinements as to the visible light wave spectrum have only recently been narrowed to offer lighting for the aquarium industry. Very energy efficient and long life before disposal make LED appealing to a segment of aquarists. Optimistically, we look forward to offerings of more visible wavelengths in the LED spectrum thus allowing aquatic plant growers and reef keepers the quality of light needed to support the environment.

General Light Guidelines Among commonly asked questions is “How long should the aquarium lights be on each day?” Because most aquarium inhabitants and plants come from tropical regions, it is best to mimic the light in this region. Length of daylight varies little in tropical areas, generally lasting 12 hours with an intense period of nine to 10 hours. Keeping lights on for more than 12 hours each day has no practical benefit and can cause algae blooms. It is best to buy an inexpensive timer and automate the light system.

The color spectrum of a lamp changes as the light ages. While the lamp may still light, it does not emit light of the original wavelength. A common problem occurs when the hobbyist uses a lamp until it no longer radiates light of the correct wavelength. Lamps should be changed at least once a year, preferably every six to eight months.

In deeper aquariums or those with more particulate material in the water, more light is absorbed or scattered, so less reaches the tank bottom. This is an important consideration in plant and reef tanks.

Depending on the tank setup, different aquaria will have different lighting needs. Fish-only tanks require only simple light systems to show off the fish and tank setup, different aquaria will have different lighting needs. Fish-only tanks require only simple light systems to show off the fish and tank setup, though the lighting can be more elaborate. The final decision depends on individual taste.

To be successful, plant tanks require correct lighting. The No. 1 reason for lack of success in growing plants in an aquarium is using the wrong lamp. Plants have two types of chlorophyll: a and b. Chlorophyll a absorbs light at 405 and 640 nm. Chlorophyll b has a peak absorption at 440 and 620 nm. Plant lamps are designed to emit light at the red wavelengths to duplicate the sun, but too much red color can cause aquatic plants to grow tall and thin. For best results, use a daylight (5,000° K) lamp in combination with an actinic white or actinic day lamp. The actinic day or white lamp is a mixture of 50% actinic (blue light) and 50% daylight. In large or deep aquaria, consider using compact fluorescent.

Successful reef aquariums absolutely require adequate light. Reef tanks contain soft and hard corals that harbor zooxanthellae (symbiotic algae). For the coral to live, the zooxanthellae must thrive. To do so, they need the correct intensity of light at the right wavelength. Actinic lights provide a concentrated light wavelength that promotes photosynthesis. If only actinic lamps are used, however, the water color in the tank will be very blue, which is not visually appealing, and the light will not be intensive enough for the other aquarium inhabitants. Therefore, a reef tank needs a combination of one actinic lamp and one or two daylight lamps.

Final Tips Generally, hobbyists do not pay much attention to lights for a freshwater fish-only aquarium and pay only slightly more attention to lights for a tank where the goal is to grow plants. If there is an algae problem, plants won’t grow or corals waste away after three or four months, improper lighting more than likely is the cause.

Remember, older lamps shift wavelengths, resulting in algae growth. Most lamps should be changed every eight to twelve months. Also remember that a deep tank needs more lighting than a smaller tank. Intense lamps are best for this situation. And finally, remember that proper lighting, selected in accordance with the guidelines and information provided here, will help your aquarium fish and plants thrive.