well let me be the first to take a crack at it in laymans terms. your gonna need a len or a chrisrd if you want professional advice. I have a 125 gallon and I have the outer orbit extreme, 4X96 watt power compacts and 3 150 watt metal halides, I probabbly should have gotten the 250 mh's intead. but it is what it is. I want to atempt a clam soon but fear I don't have enough light for one. my buddy has the 150's on a 90 gallon and has succcess so far for about 3 weeks. but it is going to take a while before I am convinced it is enough.
you are starting a 210 gallon, I heard at a minimum you want 4 watts per gallon, but I also heard between 9 to 12 watts per gallon is ideal. That rule isn't exactly it, it has to do with par value and other things. I am not the light expert just couldn't afford the light I really wanted nor did they have the style I wanted in 250's either.
not sure if I helped here or not. but your tank is deep, get enough light to get down there. I am sure you can find something online with sizing lighting fixtures for gallons and depth of tanks
article..........
Lighting is a controversial topic in fishkeeping. Most fish are not particular about lighting—the light is more for the aquarist than for the fish. However, a regular cycle of light and dark, simulating day and night, is beneficial for fish, since it establishes a routine and makes them feel more secure. Any light will do for a fish only (FO) tank. A fish only with living rock (FOWLR) tank will need a more powerful light to encourage the growth of coralline algae. There are many types of lights available; generally speaking, the higher the power rating in watts, the better. Some types include fluorescent, VHO fluorescent (Very High Output), compact fluorescent and metal halide. A powerful fluorescent lighting fixture may be enough for a fish only with living rock (FOWLR) system, depending on the depth and size of the aquarium. Coral reefs require more powerful lights, the general rule being 3 to 5 watts of power per gallon of water; research of particular species' needs before buying is essential. Metal halides are the most popular lighting fixture of reef aquariums, since they provide more light per lamp than fluorescent fixtures. Additionally, metal halide lamps produce light from a single "point source" and thus produce flickering "glimmer lines" on the aquarium floor, an effect prized by aquarists. Actinic lights produce a deep blue spectrum designed to simulate the dominant wavelength of light a few metres below the ocean's surface.
Recent advances in lighting technology have also made available a completely new technology in aquarium lighting; Light Emitting Diodes (LEDs). Although LEDs themselves are not new, the lighting temperature which used to be very low on LEDs has now been increased to the point where LEDs can be used as a viable alternative to gas and filament based lighting. LED lighting is still in its early stages and therefore very expensive, however there are several advantages that these lights bring over traditional lighting, barring the initial cost; they consume very little power, in being solid-state they have an exponentially longer lifespan- and do not need to be replaced, and because the "light fixture" is comprised of hundreds of small bulbs, these can installed and controlled by a microcomputer to slowly fade in and out to simulate day break and sunset, as well as having the ability to mix in special blue LEDs which can simulate the moon at night, also with the programmability of having the phases of the moon.
When considering lighting for an aquarium, there are generally 2 factors to consider. a) Wattage/Power b) color temperature. Depending on the type of lighting i.e. flourescents, MH etc, the wattage of light emitted varies: 18W, 36W, 150W 250W etc. Wattage is equivalent to power and in lay mans' terms, it determines how bright and strong the light will shine. The deeper and bigger the aquarium the higher wattage you'd need. Color Temperature refers to the spectrum of light being emitted by the lamp and they're measured in degree Kelvin (K). Again in lay mans' terms, this refers to the type of light. Light from the sun has a color temperature of approximately 6500K and they're perfect for growing plants in refugiums. 10,000K light appears white and will give good coloration to fishes and corals. Moving up the spectrum there is 14,000K and 20,000K bulbs that produce a bluish tint that mimics the lighting conditions under the sea creating a great environment for lifestock in the aquarium.
