Metal Halide aquarium lights are the brightest
form of aquarium lighting. If you are planning on keeping healthy
clams, stoney corals called acropora or millepora it is nescessary
to have the brightest most intense of aquarium lighting and metal
halide aquarium lighting is the answer. The need for light intensity
provided by metal halides becomes important as tanks become deeper.
Generally, metal halides are practical for lighting reef tanks
that are 16 or more inches deep and becomes a necessity for tanks
deeper than 18 inches. Even shallow tanks with the more demanding
corals, such as stoney's should go the way of metal halide lighting.
There are two types of metal halide aquarium light bulbs: the
first is the first called single ended or single based (commonly
referred to in the industry as mogul based). The second metal
halide light bulb type which has become very popular are called
double ended (commonly referred to in the industry as HQI bulbs).
Metal halide lighting needs to be changed anywhere from every
9 to 12 months. For metal halide lighting to be effective it
is required to have one bulb per two foot of aquairum. The wattage
you will use totally depends on the depth of the aquarium. The
intensity of light decreases by the square of the distance that
area is from the lighting source. In other words, if you double
the distance between the light and the organism, you will quarter
the amount of light reaching the organism. As a general rule,
175 watt metal halide bulbs are the best choice for aquariums
that are less than 20 inches in depth. Tanks that go from over
20 inches to up to 28 inches in depth, we recommend a 250 watt
bulb be used. Aquariums any deeper than the 28 inches call for
a 400 watt light bulb.
Many people find metal halide aquarium lighting
more attractive than fluorescent lighting types such as VHO or
power compacts. Why is metal halide more attractive? In natural
reef environments surface waves act as a lens that focuses light
and create "glitter lines." These glitter lines, familiar
to divers, appear as flashes of light of high intensity and short
duration and are very attractive to the eye. In reef aquariums
these glitter lines, or flashes, can be created through the use
of point source lights, such as metal halide lights, and surface
agitation of the water. Fluorescent lighting is more diffuse
and does not create these effects. Whether this flashing light
is advantageous to the corals is not known.