Basics : Lights
Lighting is for you and natural plants. Fish will get along fine, establishing a sleep cycle and doing everything else using only the indirect lighting from windows, but they really prefer that the light originates above them (they try to orient their bodies to the light source). Direct sunlight is an undesirable light source and normally avoided, otherwise algae issues will be difficult to manage.
Another lighting aspect to remember is that fish have no eyelids to shield them from sudden changes in brightness. In a dark room, the tank lighting should be staged upwards progressively, or the room lights should be turned on for several minutes to allow the fish to wake up and adjust. Fish eyes are very similar to our own, with colour cones & depth perception. You only need to imagine the effect of being awakened by a bright light, and not being able to close your eyes, to appreciate their discomfort.
Generally speaking, select a lighting set-up which best matches your plans when you buy a tank. Planted aquariums benefit from lots of light. Non-planted tanks are fine with conventional lighting. If you know you will be growing plants, then look at fluorescent lighting above 0.8 watts per gallon (wpg).
Details...
Briefly below are comments on incandescent, fluorescent, fluorescent life, fluorescent types, light upgrades, fluorescent canopys and how much light to use, and a plethora of articles can be found in the lighting links.
INCANDESCENT
Incandescent lights (short cylindrical tube with a screw-in base) are not very suitable for plant growth, and they can generate enough heat to warm a small tank undesirably (tank temperature should not change more than 3F in a 24 hour period). The light spectrum from incandescent lights is also very narrow, so your fish's colours will not show as nicely. The intensity is very poor as compared to fluorescent lighting, so it will be far less brighter, especially with deeper tanks. Other than these limitations, they work. With incandescents, consider using a lighter colour of substrate to reflect up and brighten the tank.
FLUORESCENT
Fluorescent lighting has become the mainstay for aquariums due to the light spectrums available, the lower running costs, the lower temperature (most of the heat is from the ballast), and the higher intensities available for the space inside a conventional aquarium canopy.
FLUORESCENT LIFE
Fluorescent lamps are typically tube type (changed every 8-12 months if used for growing plants) or compact fluorescent (typically changed at around 3-4 years if used for growing plants). When not used for growing plants, then all fluorescents are changed at the hobbyist's discretion. With aging, there is a reduction in certain light frequencies but the effect is not readily seen by the human eye. Plants may reaction negatively at some point, so then the lights should be replaced.
FLUORESCENT TYPES
Fluorescent tubes are rated by wattage (typically according to their length at about 0.8 watts per inch), and come in an assortment of diameters (T6, T8, T10 and the most common T12). A smaller diameter allows more lights to fit under a canopy. Thinner tubes are typically more expensive but have a higher efficiency (lumens of brightness). Spectrum (colour, in Kelvin) and CRI (accuracy) are used for comparison between products. Compact fluorescents have similar characteristics, but with their thinner diameter, and the ability to double back or be more tightly condensed, they will typically yield higher intensities.
LIGHT UPGRADES
There are other lighting systems available for aquarium lighting, but beyond the scope of this web site. I really want to keep to the title of this page (Basics). However, the majority of upgrades are done with some type of fluorescent lamps. How you upgrade depends on the system you have now, and your budget. When building DIY canopys, standard tubes are used, or compact fluorescent (CF) lights (typically for smaller or odd shaped canopys). For CF supplies AHsupply.com is often referenced in the newsgroups, but I have no experience with them.
FLUORESCENT CANOPYS
There are basically 4 types, strip light, polo light (over a glass cover), sealed tube lights and DIY (over a glass cover).
Strip lights are housed in a plastic shell containing the ballast. It uses a glass insert in the canopy between the tube and the water to protect it's connections from corrosion. There is no practical way to upgrade this system. The most conventional upgrade would be to replace the canopy with a glass cover and add polo light(s).
Polo lights are also housed in a plastic canopy with an integrated ballast, but they float on a full width glass cover, or slide back and forth along the tank's end rim. Adding a 2nd polo light is a quick upgrade, but will crowd access for feeding and equipment. When using multiple polo lights which come right to the front of the tank, feeding is simplified by leaving an opening in the back with the equipment (rather than removing the front polo light to open the glass cover). Automatic feeders work well in this configuration. Polo lights also come in high output configurations with multiple tubes and CF configurations.
Sealed tube light canopys are a recent introduction to the market. The tube(s) are fixtured inside a plastic canopy, with a sliding gasketed cover for the tube ends. This has the advantage of eliminating the protective glass pane which reduced the light level and needed to be cleaned periodically. This design also allows the full width of the tank to be used for longer tubes, (unlike strip lights), and the canopy is more open under the tube, resulting in more light to the tank. The drawback is the fixturing is fixed, so upgrades are not practical. These canopys appear on rimless tanks, which will not accept a conventional glass cover (no rim to hold the glass), so upgrades are very difficult.
DIY is typically standard fluorescent tubes inside a custom made wooden box painted latex white on the inside. Variations on this theme are to use CF lights for higher intensities. It is also possible to use sealed tubes and forgo the glass cover entirely, but this brings humidity issues to the underside of the usually wooden canopy. Condensation in a canopy dripping back into the tank can be a source of toxic pollutants. DIY canopys are ideal for getting exactly the light levels and spectrums you want, for an economical price. As soon as your tank length is 48" and longer, commonly available 4' fluorescent tubes are available at low cost. Using multiple tubes will spread their light spectrum, so you do not need to purchase the more expensive specialized tubes. Note the different life expectancies between regular and CF lighting and figure out what works best for your application. When running high amounts of fluorescent lighting, consider keeping the ballasts outside the canopy, or providing sufficient ventilation to prevent the heat from warming the tank excessively.
HOW MUCH LIGHT
What is deemed to be the correct amount of light varies tremendously by different hobbyist's experiences and expectations, and is typically only an important subject when growing plants. There are plants which are categorized as low-light, medium-light and high-light, so results will vary according to the light intensity/duration and the type of plants selected. Plants are also very adaptable, and if all other conditions are good, plants will react to non-ideal light levels by reduced growth, or an atypical leaf formation. A tall stringy plant with tremendous growth at the water's surface is an example of adaptability for a plant which is more typically short & bushy.
It is reasonable to assume that light levels below 1 watt per gallon (1 wpg) will limit growth rates somewhat. This can be compensated for by using lower-light plants. Light levels above 2.5 wpg will typically exceed the plant's requirements and can result in an algae growth which would be difficult to control. Above 2.5 wpg, it is recommended to inject CO2 into the tank, such that the plants will be able to utilize the higher light levels. Using CO2 injection, light levels above 3 wpg are not uncommon. Low-light plants might 'melt' or 'burn' under high light conditions. CO2 injection has a limited effect in low light levels (under 0.5 wpg). When growing plants, the typical light duration is started at 12 hours per day, and then adjusted shorter or longer according to results. The following search engine (by Soren Peterson) allows you to enter your light range and other parameters, and have the corresponding compatible plants listed.
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