Well Im still hanging in here trying to learn and glean, just abiding my time when I can join the "I have a Saltwater Fish tank" club.  But, until then I have another question.  I have been trying to study up on different lights and the such and I am wondering what makes one type of light better than another.  Is it solely the K rating or is it wattage as well?  What is a good K rating to use?  I have seen the daylight bulbs in stores that have a K of 6500 but they are cheep?  Is that not a good light or is a higher K needed?  Also what wattage is recommended for a tank?  Also why are metal halides better than other lights? Is it that they have a higer K or wattage or is it just the intensity of light they put out.  I am mostly interested to hear what people have used and has worked well for corals they have.  Thanks.

I have 4 VHO 36" lights over my 75 gallon tank.  I have had good sucess with Xenia Elongata, Blue-Green Zoanthids, Orange branching Montipora, green star polyps, ricordea, brown montipora, scroll?? plating?? montipora, and bubble tipped anemones.

VHO or PC lights are great for mid to slightly high light demanding corals, but if you are looking at the really high light demanding corals you then want to go with metal halid lighting.  Most people that use MH lighting use actinic lights to provide more blue light as it is more apealing to look at.  That is why with MH lighting they always go with a higher kelvin rating as they provide more of the blue light.  This blue light is also important to the growth of the corals as the zoanthelia algea need the blue light for photosynthesis.  The lower the kelvin rating the more red light is present, and the hair algea and other undesirable algeas flurish under this spectrum.  Typically the low end is about 6500 kelvin, but most recommend 10000 kelvin bulbs as they provide more of the blue light that the corals need.

The wattage of the bulbs is important as it is a good indicator of the lumens (the intensity and quantity of light).  Even though people will disagree with me, but MH lights are not the 'premier' lighting for reef systems.  The advantage they provide is you can get more light out put for the area they take up.  As an example, I have a 75 gallon tank and I can put about 440 watts of VHO lighting above it.  If I were to use MH lighting I could have 800 watts because I could use 2 400watt bulbs.  The big disadvantage of MH bulbs is the cost of the bulbs and the heat that they produce.  Most people using MH lighting have to use chillers to keep their tanks cool.  That is why I went with VHO lighting as they do produce heat, but not nearly as intense as MH lights and it is a cheeper setup to maintain.

VHO vs PC lights I went with VHO because with the IceCap balasts you could use regular bulbs if needed.  Also the cost of the bulbs for VHO is less than the PC, and it can get a little complicated when replacing PC bulbs as there are a few different configurations.

Most people, myself included, that use florescent lighting use an even mix of 50/50 bulbs and actinic bulbs as it helps provide the blue light the corals need.

VHO is what GARF use (http://www.garf.org">www.garf.org is a neat website) and they get excellent results.

I would not use two 400 watt MH over a 75 gallon tank. That's way too much light. One or two 250 W MH with two VHO actinic would do nicely for acropora and clams, in my opinion. Actually acropora and clams grow nicely with CF too. And you can always give your tank real sunlight. They used to recommend no direct sunlight because of unwanted algal growth, but now that there are plenty of herbivores... and theres nothing like the color brilliance reflected by natural sunlight, in my opinion.

Just so you know where I'm coming from, I'm the guy that uses six regular output (40 W) fluorecent tubes on my 75 and it looks great(but no acropora or clams)(see the gallary). I am also a doityourselfer that takes used ballasts, underground sprinkler wire, a soldering gun and silicon to make lights!

Try this next time you change fluorescent lights.

17% white or white/actinic (actinic is the fancy word for blue light of around 420 nanometers in wavelenth, the spectrum that coral need to really do well)

66% actinic

17% plant grow bulb

Plant grow bulbs grow coraline algae like crazy and brighten the blues greens and reds of fish, coral and algae!

If you buy the CF smart bulbs use the combo of blue/plant growth rather than blue/white, or one of each if you use two.