Lighting

Regular cyclical lighting is used in aquariums to simulate day and night. This is beneficial for fish and invertebrates since it establishes a routine, enables them to rest, and makes them feel more secure. The lighting used varies depending on the inhabitants of the aquarium. Typically, the type of lighting for aquariums with fish only is regarded as unimportant. In aquariums containing invertebrates, however, where algal growth (of both free-living and symbiotic algae) is desired, more intense lighting is required. There are many types of lights available: some common types include fluorescent, VHO fluorescent (Very High Output), compact fluorescent, LED and metal halide. Actinic lights produce a deep blue spectrum designed to simulate the dominant wavelength of light a few metres below the ocean's surface.

Many different sources make different claims about what type of lighting system is the best. In reality, each technology or variation has its own advantages and disadvantages. The most primitive lighting source is natural sunlight. This is only effective in areas near the equator because the intensity of sunlight is greatest there. Efficiently utilizing natural sunlight requires complex planning and is usually utilized on only the largest reef systems. The next step up in technology is incandescent lamps. These are very wasteful of energy, producing between 15 and 30 lumens per watt of power (Out of a possible 683 lumens per watt for an ideal light source). Standard fluorescent lamps offer a great improvement over incandescents. There are better colour temperatures available in fluorescent tubes that are more suited to aquariums than those of regular light bulb. They are also more efficient, averaging between 90 and 95 lumens per watt. The downside to regular fluorescent lights is that they do not have the intensity to penetrate into deeper aquariums. There are a number of improved variations of fluorescent technology. The main ones are very high output (VHO), power compact fluorescent (PC), and T-5 high output (HO). VHO lamps are fluorescent lamps run at higher power levels, usually about three times the standard wattage for a given bulb length. They have the advantage of high light output, but the larger diameter bulbs limit the efficiency of reflectors. PC lighting is also high-power fluorescent lighting, but the bulbs are folded to put more tubes in a given space. The output of PC lamps are reduced by inefficient reflector designs. VHO and PC bulbs are also fairly expensive to replace. T-5 HO lights are the newest variation on fluorescent lights. They are run at slightly higher power levels than standard fluorescent lamps, but are made significantly thinner. This allows for more efficient reflector designs that get more light into the aquarium. Because of this, higher quality T-5 systems often match or exceed the output of equivalent compact fluorescent or VHO lighting fixtures. All types of fluorescent lighting offer the same efficiency in lumens per watt; it is the shape of the bulb and reflectors that makes their overall outputs different. Metal halide lights are the next level up from fluorescent technology. Metal halides produce about 90-100 lumens per watt of power. This is roughly the same as fluorescent. The improvement with metal halides is that they concentrate this light output into a very small space, whereas fluorescent lights evenly illuminate the entire aquarium. This is often referred to as point source lighting, and is what causes the rippling visual effect on many advanced aquarium setups. This concentration of light output increases the intensity, allowing metal halide lamps to get a lot of light to even the very bottom levels of most aquariums. Metal halides are available in many color temperatures, from 6500K up to 20,000K, though bulbs as high as 50,000K are occasionally found. The downsides of metal halide lighting are the cost and the heat produced. Most metal halide fixtures are more than double the price of an equivalent wattage fluorescent system, though prices have begun to drop in recent years. Halide lamps concentrate heat as well as light output. The surface of an operating lamp becomes hot enough to cause second or third degree burns instantly, so this lighting technology must be used with caution. The heat produced can also warm the aquarium to unacceptable levels, often necessitating the use of a chiller. The most recent addition to the list of aquarium lighting technologies is LED lighting. These have the potential to be much more efficient than any other technology, but have not yet become so because of issues of heat dissipation. LED's have the advantage of point source lighting, but are also completely dimmable at any power level. This allows for more advanced lighting schedules, even the simulation of cloud cover. So far, LED's have found use mainly as lunar lighting.

When considering lighting for an aquarium, there are generally two factors to consider: wattage and color temperature. Depending on the type of lighting (i.e. fluorescents, metal halide, etc) the wattage of light emitted may vary considerably, from tens of watts to several hundred watts in a lighting system. Wattage, while not indicative of color, is equivalent to power and essentially determines how brightly the light will shine. Due to the scattering of light in water, the deeper one's tank is, the more powerful the lighting required. Color temperature, measured in kelvin (albeit slightly unrepresentively) refers to the color of light being emitted by the lamp and is based on the concept of blackbody radiation. Light from the sun has a color temperature of approximately 5900 K and lighting systems with color temperatures >5000 K tend to be best for growing plants in both the marine and freshwater setting. 10,000 K light appears bluish-white and emphasizes coloration in fishes and corals. Higher up on the spectrum there are 14,000 K and 20,000 K bulbs that produce a deep blue tint which mimic the lighting conditions underseas, creating an optimal ambience for invertebrates and livestock present.