Obviously with a plethora of different type of lighting systems to choose from, trying to figure out what tube to use can be a nightmare. Largely it depends on what you are trying to illuminate, and what your budget it.

It also depends on what size tank you are trying to illuminate, not so much as surface area or footprint of the tank, but depth of the water. The example setups below are for four 15 gallon tanks turned sideways so that a four foot fixture across the top will illuminate all of them. Double the amount of light for deep tanks greater than 18 inches.

Many small aquariums have a small plastic or metal hood that has one or two tube shaped incandescent bulbs. For the bulbs to provide enough light to grow plants they need to be of such high wattage that there will be a severe and deleterious effect of the fish by the massive amount of heat being given off from the bulbs.

Incandescent illumination, although inexpensive in initial setup cost is not recommended for aquaria. The heat generated by these light bulbs almost always adversely affects the temperature stability of an aquarium. The cost to operate is fairly high, and the quality of light is poor compared to every other lighting system. Having said that I have seen some setups using incandescent lights that worked well. Plants were healthy, the tanks were not that hot. Be that as it may, if you get good results with incandescent lights you will get better results with fluorescents. Some of the smaller halogen bulbs are useful for supplementing fluorescent lights, as the halogens, because they are still incandescent, put out quite a bit of red light. Not only does this help to balance the spectrum, but it has a more pleasant esthetic appearance.

Theoretically a 300 or 500 watt halogen lamp can be suspended a foot above the tank, and this would provide enough light without cooking the fish, but 500 watts is a lot of energy; a 175 watt metal halide bulb will provide the same amount of light for a lot less energy. The only practical use for incandescent lights would be in a setup that was primarily fluorescent. A couple of small halogen bulbs, if well shielded from water splashes would provide the red light so needed by plants.

Fluorescent lights are the most economical way of lighting an aquarium in the long run. Once the initial purchase of the fixture is made the low cost of operation and long life of the tubes makes fluorescent light very attractive. For a beginner tank that has an incandescent fixture the new compact fluorescent bulbs with integrated ballasts will, in many cases, screw right into the existing incandescent ballast. Bulbs for these are available from 2700K to 5000K color temperatures, although as of this writing only Osram makes 5000K compact fluorescents.

The absolute cheapest setup is to buy whatever fluorescent tubes are on sale at the local hardware store. Usually cool white. This is far from the best, but it will work. One cool white and one warm white is a little better, although one plant growth light and one daylight bulb is still a fairly cheap setup, (both are well under $10) with quite good light quality. For growing plants, a setup consisting of one plant light, two wide spectrum plant lights and one chroma 75 (or equivalent) will provide the right amount of the correct type of light. Triton (or equivalent) tubes could be used of cost is no object. If the pinkish color is objectionable, two Ultralume 3500 and two Ultralume 5000 can be used instead of the wide spectrum plant lights.

For keeping African Cichlids, or any other fish that is used to a lot of light, two (or four, depending on preferences) chroma 75's can be used.

Low light fish such a killifish and dwarf Cichlids will do best under two Gro-Lux or if they have an abundance of plant cover, two Gro-Lux wide spectrum tubes. These tubes will not frighten the fish with a lot of light, and they should encourage good plant growth to provide much needed cover from the light. As an aside, I have kept certain killifish such as Aphyosemion australe, A. gardneri, and A. sjoestedti under the setup described above for plant growth and they didn't seem to mind. Some species of fish do not like a lot of light and in the wild will hide under cover to avoid intense light. In an aquarium with bright light and without some cover to take refuge they will be as stressed as if they were forced in the wild from their shady environ to an area on bright light.

Marine invertebrates and certain freshwater plants have very large light requirements, and for these, an HID lamp would probably be the most appropriate. It is unlikely you could put enough fluorescent tubes on top of the tank to supply enough light, or if you could you may have spent so much on VHO lamps and ballasts that it would have been cheaper to install a halide lamp in the first place.

The cost of the HID lamps is pretty large, and even worse, the more useful lamps to growers of plants are even more expensive. Usually mercury vapor or sodium vapor lamps are available at semi- reasonable rates from hardware stores where they are sold as security light; especially in rural areas. I have heard of people trying sodium vapor lamps, but have never heard of any success with them. People have had some mixed success with mercury vapor lamps. Metal halide lamps give very good results, but are the most expensive and difficult to obtain of all the HID lamps.

For applications requiring a REALLY BRIGHT light, the current GE lighting catalog lists a 10,000 watt carbon arc lamp used for lighthouses.