lighting

Lighting
A DIY metal halide pendant lampRegular 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. Aside from establishing a routine, high output lighting is required for many invertebrates such as corals and anemones to survive. Lighting in marine tanks that contain only fish and live rock is not an important issue. In aquariums containing invertebrates, however, where algal growth (of both free-living and symbiotic algae) is desired, more intense lighting is required. Various light sources include but are not limited to: natural sunlight, fluorescent, VHO fluorescent (Very High Output), T-5 fluorescent, compact fluorescent, LED and metal halide. Each type of lighting has its own advantages and disadvantages. They all vary in initial cost, maintenance cost, spectrum obtainable, longevity, efficiency, and power.

Natural sunlight
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, as such, this method is applied on only the largest reef systems. Many times in the hobby natural sunlight is actually avoided due to the low spectrum of lighting it has. The yellow tint is often undesirable and can encourage bad algae growth.

Incandescent
Incandescent lamps have been phased out over the years. They are 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). They can be found many times in older aquarium light hoods. They burn out frequently, put off a lot of heat, and normally do not have an appropriate spectrum associated with them. Most incandescent lamps can be replaced with commonly available and efficient screw in power compact bulbs.

Standard fluorescent
Standard fluorescent tubes are the common light bars you find in commercial ceilings. Fluorescent lighting has more color temperatures available which are more suited to aquariums than those of incandescent bulbs. They are also more efficient than incandescent lighting, 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.

Higher output fluorescent
There are several improved variations of fluorescent technology. The main ones are very high output (VHO), power compact fluorescent (PC), and T-5 high output (HO).

VHO 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 and the number of bulbs that can be fit in an aquarium hood.
PC lighting is also high-power fluorescent lighting, but the tubes are thinner and are often folded over one another to reduce size. Most spiral shaped energy efficient light bulbs commercially available for house lighting are power compact fluorescent bulbs. PC bulbs are recommended to be replaced every six months to a year to keep the desired light spectrum.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 than standard fluorescent bulb. This allows for more efficient reflector designs that get more light into the aquarium. Higher quality T-5 systems often match or exceed the output of equivalent power compact fluorescent or VHO lighting fixtures. On the downside, T-5 lighting is the most expensive type fluorescent lighting available. Many times it is much cheaper per watt, especially in the long run with the multiple T-5 bulbs being replaced, to go with an equivalent metal halide light setup over a T-5 setup if such high light output is requried.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
Metal halide lights are generally the highest output lighting commercially available. They 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 penetrate light to even the very bottom levels of most aquariums. Metal halides are available in many color temperatures, from 6500 K up to 20,000 K, though bulbs as high as 50,000 K are occasionally found. The downsides of metal halide lighting are the initial cost and the heat produced.
Most metal halide fixtures are more expensive than fluorescent systems, but are required for some reef setups. 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, possibly necessitating the use of a chiller for certain aquarium setups.

LED
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 are not fully developed. LEDs have the advantage of point source lighting, but are also adjustable to most power levels. This allows for more advanced lighting schedules, the simulation of cloud cover, or even lightning storms. So far, LEDs have found use mainly as lunar lighting in commercial products.
Reef-keeping enthusiasts have began to build their own LED light fixtures as well. Debate over their effectiveness towards coral is still inconclusive, particularly with respect to their ability to give off UV radiation, critical to obtaining a vibrant array of colors that most people interested in LED lighting are looking for.
LED lighting can be considered one of the most energy efficient and low impact options to lighting a reef tank as well, with a projected life expectancy of seven years.

Overall lighting considerations
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 kelvins (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.

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