Not only is lighting very crucial to the life, and maintainance of symbiotic corals. It is also pertinent to all other reef inhabitants to some degree. Symbiotic sponges, photosynthetic microorganisms, inverts, macro and coralline alll are dependent on good lighting.
It is a very expensive inverstment to the reefer world, one in which many try to cut corners and save a buck or two, only to have detrimental results. Skimping on lighting requirements in an effort to save money, hoping on a wing and a prayer that the lighting you just purchased is adequate enough to support coral life is truely a game of "Russian Roulet".
You see, most of the corals that you see for sale at lps are from shallow water depths(to15feet). Therefore the light intensity from the sun to the coral is intense!! So why would you try to get by with 1 watt per gallon of light. Think about this-on a clear sunlite day in the Caribbean, the light is so intense that it is almost impossible to replicate the kelvin of the suns rays to the awesome corals below.
Basically, what i'm trying to stress is, don't try to save a buck in the hopes of creating the perfect coral reef by using less than optimal lighting on your reef tanks!!!!!!!!!!!!
The other thing I would like to mention to all of you, which was very informative is:
The most intense light from the sun happens within the first 3 feet of water. Within the first 15 feet of water the red and orange color of the light spectrum have been filtered out. By 30 feet deep, yellow light has been altered. After 50ft., the green light from the sun has been filtered, thus leaving the blues and purple light in the spectrum from say 440-490nm. Basically, what is being displayed is how fast water reflex sunlight's wavelength. Remember, sunlight has a color temp of 6500-6900k which is a very cool temperature. As you approach the 20000k end of the spectrum(blue)the temperature of the light is hotter(gets higher as the water depth increases).
Now the last thing which is COOL and very informative when trying to decide what part of the lighting spectrum you want to represent your reef tank. Replacement of light bulbs based on spectr and intensity: for flourescent bulbs about 6 months. Vho light even sooner than that. Metal halides should be replaced approximately once a year. Power compacts may keep their intensity for 12 to 14 months before replacement is necessary.(remember!!!!!, bulb light to the eye will probably look as bright as when you first bought them!!!very misleading as the specra and intensity, Wattage decreases usually over a short period of time. Don't make the mistake that I did by using bulbs longer that expected, or your corals fate will be null and void as they will soon start to parrish.
One last thing before I create a book longer than" Moby ****". Bulbs in the red end of the spectum tend to cause microalgae problems as well as coral bleaching problems, however the intensity tends to last longer. Tanks higher in the spectrum towards the blue end tend to increase the growth rate of corals and cut down on unwanted algae, but need to be replaced sooner than the red, yellow orange spectrum bulbs.
Remember to keep the glass tops clean(no salt creep etc.)to allow the greatest light intensity. Also, carbon and foam fractionators(protein skimmers) offer cleaner water which helps to increase light intensity to your tank.
Just be careful not to do anything drastic! Change bulbs over weeks, not all at once. Also, if you purchase corals at a lfs that displayed the coral you purchased in dimmer light than your tank-start off by acclimating the corals lower to the bottom of your tan k then raise them up. Conversely, if you purchase corals displayed with 450watt mh's then buy and bring the coral home and place the coral in 150 watt mh tank place the coral toward the top of your tank to not stress or bleach your prixe possession.
Well, I'm done and need to have a beer and therapy on my hands.
I hope this helps clear lighting up for you as it did for me...Maybe I can get some money from these lighting companies for making everyone buy more lights!!hahahaha-No seriously-this will help you trust me!
Lighting 101 for all reefers!!very informative!!! 
jb
