Well, I remember by first, and only, intimate experience with a woman. It was years ago in a bar in L.A. She came over to me in her fishnet stockings, short skirt and whispered in my ear the immortal words,
"Hey big boy got a light?". Well after the most exciting five minutes of my life I left her room and looked at my, now near empty, wallet. Then it dawned on me. For what that five minutes had cost
"I could of had some of those new fangled actinic lights for my tank!!!" 
I have left out lighting until this point, as until you start stocking your tank it is not all that important. If you bought a complete set-up it probably came with a hood and fluorescent lights. To keep LR and fish alive you really don't need much more.
Coralline on LR is a low light alga so it doesn't require megawatts to sustain it. Fish, for the most part, are pretty much indifferent to light levels.
The bulbs that come with most tanks are standard fluorescent types that you can get in any Lowe's or Home Depot. The drawback is they have a K value of only about 4000-4500. Not a very good level for a marine tank.
So you say, "What the expletive deleted is a
K?"
K stands for Kelvin, which is a temperature scale in the metric system. It is similar to Celsius but zero starts at absolute zero. Armed with that bit of trivia you say, "So what!".
The use of Kelvin ratings for illumination comes from the photo industry. They needed a scale to measure the apparent color of light and chose the K scale to do it. To understand it, picture a black ball suspended in an inert atmosphere. We start to heat it up until it glows. At first it becomes red hot, then orange, yellow white and so on as it gets hotter. The temperature that is needed in Kelvin degrees defines these changes in color. That standard fluorescent used around the house gives off a Kelvin of around 4500 K. This is a decidedly yellow color. Experiments with reef tanks have also indicated that the wavelength (I'm not even going to touch angstroms and such
) produced by such a low K value is not conducive to good critter growth in our tanks.
Now there are some household type fluorescents that have fairly high K values. The Opti-lume daylight series comes to mind. These are fairly cheap bulbs and have color outputs closer to 6500 K. This is pretty close to the K temp for sunlight. If you can find some they are a better solution than the "standard" bulbs. You can also buy bulbs especially designed for aquarium use over the Internet or at the LFS. They cost more than the household bulbs but have higher K values, as high as 20,000 K, which produces a very blue light. To me the real high K tubes are too blue. I prefer the lights with a range 8000-12,000 K which is more white than blue. As far as your tank is concerned it doesn't make much difference. The blue light is just as good as white. What K value you use is a matter of what looks best to you. One other thing with high K fluorescents tubes is that higher K lights give off less illumination than lower K tubes. You may opt for a 10,000K over a 20,000K just because you get more bang for your energy buck with the lower K tube.
Let's take a second to see how a fluorescent tube works. The tube has a starter element on each end and is filled with a gas that contains a small amount of mercury. When we turn it on an initial surge of high voltage is sent to the tube and creates a flow of electrons from the elements. This causes a current to flow through the tube and produces a cloud of ionized particles. The inner part of the tube is coated with a phosphorus compound. Electrons in the ionized cloud strike the phosphorus and cause it to glow creating light. Now, when the current starts to flow in the gas inside the tube, the resistance drops real fast. The amount of current would increase and the tube would glow brighter and brighter. It would do that until it burned itself out in very short order . Enter the ballast.
You've all seen a ballast, at least I hope. It is the brick like thing inside the hood of a fluorescent light. It serves two purposes. First is contains a capacitor or some other circuit that provides the initial high voltage to get the lamp started. Once the lamp is started it contains a coil, called a choke, which limits the amount of current (called impedance for those that dig tech terms
) that will go to the lamp and saves the lamp from burning up.
In our discussions of aquarium lighting we will be dealing with ballasts. And, as usual with everything in this hobby, we will be dealing with several types, some which do the very same job but in an entirely different way.
Enough about ballasts for the moment. Let's get back to the lights themselves. The household type fluorescent is called an N.O. or normal output type lamp. N.O. lamps use 10 watts for every foot of length. That is a 24" is 20 watts and a 48" is 40 watts. That is for a T12 bulb. "A 'T' what?" you say. Well the T number is the diameter of the bulb in eighths of an inch. Household type bulbs are usually T12's that means it is 12/8
ths or 1Ã"šÃ‚½ inches. The other common sizes are the 1" T8 and the 5/8" T5.
For the reefer that only is going to keep fish or some of the lower light soft corals, then N.O. lighting may be sufficient. For those wanting a more diverse tank, more bang for the buck will be needed.
We'll talk about that next time.
They have candlepower, lux, lumens and PAR; all with different units and measurement methods. One of my favorites is PAR or Photosynthetic Active Radiation. If you have a gadget called a Quantum meter in your reef tank test kit bag then you are ahead of the rest of us who have no idea of the number of micromoles of quanta per second per square meter entering their tanks at the moment. 
