Lighting is very important to the health and growth of fish and plants. By far the best light for the aquarium is natural sunlight. It is difficult to match the intensity, and color spectrum of natural sunlight. Typically we keep our aquariums indoors, so the best we are able to do is to provide a few hours of natural daylight a day by where the aquarium is positioned. In most cases, we end up positioning the aquarium in a location where it receives no sunlight.
The author's 60 gallon (228 l) cube aquarium receives about one hour of sunlight in the morning during winter months. Nitrate accumulation drops significantly when the aquarium receives sunlight.
There is long running myth in the hobby about sunlight being bad for the aquarium. Sunlight is often blamed as being the cause of excessive algae growth. Algae only grows excessively when the aquarium water has excessive nutrients. In an aquarium with excessive nutrients, algae growth is actually making the aquarium ecosystem healthier for fish, by removing nitrate and phosphate that can suppress reproduction, growth, and the immune system. As long as you are able to keep the aquarium from overheating from sun exposure it is by far the best source of light for maintaining a healthy aquarium. Planted aquariums that receive several hours of sunlight every day often have very little algae growth.
Often when you buy an aquarium it comes with a standard fluorescent light with one or two rows of bulbs. Standard fluorescent lights typically are too low in intensity to help keep nitrates low or at 0 ppm. There are several alternative lighting systems that should be used instead of the standard fluorescent light, compact fluorescent (CFL), high output T5 fluorescent (T5 HO or HO T5), high intensity discharge metal halide (HID), hydrargyrum quartz iodide metal halide (HQI), and light emitting diode (LED).
The distance of the lighting system from the surface of the water should be considered when setting up the aquarium. The closer the light is the the surface, the greater the light penetration into the water. Lights placed close to the water level can transfer a lot of heat to the water, and the light distribution in the aquarium may be too focused.
The benefit from advanced lighting systems is that they can help bring out the natural colors of fish. The bright light helps intensify the colors in many species of fish, including tetras, livebearers, goldfish, loaches, gouramis, barbs, rasboras, and cichlids. Anyone that has kept goldfish in an aquarium for an extended period of time in a dimly lit aquarium, and then moved the fish to an outdoor pond, knows how bright light can intensify color.