sunlight is actually avoided due to the low spectrum of lighting it has. The yellow tint is often undesirable and is believed to encourage problem algae, though studies show it does not. 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 bulbs, which 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