Well, there is an awful lot to light, and how it can be effective for our tanks. I'll start with answering your questions, and we can go from there.

What does PAR mean? -
PAR stands for Photosynthetic Active Radiation. It's a measuerment of the number of photons between 400nm and 700nm, which is the range of visible light. It's a measurement used to estimate the growth potential of a light source. It can be a useful measurement when comparing different lights, but shouldn't be taken as an absolute measurement. Reason being is that all photons in the visible spectrum are all treated equal. Corals don't use all photons equally for photosynthesis, so PAR measurements don't always show the true nature of the light.

What does nm mean? -
Nm stand for nanometers (1x10^-9). In this application, it's a measurement of the wavelength of the light. Visible light goes from 400nm (violet) to 700nm (deep red). Below 400nm, you have UV-A (315-400nm), UV-B (280-315nm), and UV-C (100-280nm). Above 700nm, you have infrared light.

What is a wavelength? -
Wavelengths are measured in nanometers, and represent the different colors of light in this application. For example, light with a wavelength of 455nm is what we consider royal blue in the LED world. 525nm is green, and 630nm is red. Now, colors span a range of wavelengths, and change their hue depending on the direction you go. If we start with 455nm (royal blue), and add 20nm, you get into the cool blue range. Subtract 20nm, and you have deep blue/violet.

What light is best for a reef system? -
That's a highly debatable topic. There are so many options out there, and all of them have their pro's and con's. Many consider metal halide to be the "best" type of lighting, but it doesn't mean that everything else is crap. There are so many factors to consider when comparing lighting types, that we could be here all day. I'll give you a brief run down of what is commonly available:

Metal Halide:
  • High output
  • Decent efficiency
  • Pleasing appearance
  • Good overall color
  • High heat
  • 12 month bulb life


T5HO (NO isn't powerful enough for reefs):
  • High output
  • Higher efficiency than MH
  • Wide variety of color options
  • Less heat than MH
  • 8-12 month bulb life
  • Highly dependant on reflector quality for performance


Power Compacts:
  • Medium-high output (depends a lot on the bulb)
  • Similar efficiency to T5
  • Cheap
  • Bulbs come in smaller sizes than T5
  • Limited color selection
  • Poor performance compared to T5 because of bulb restrike issues
  • Reflectors don't help as much as they do with T5 (has to do with bulb shape)
  • 6-8 month bulb life on average


LED:
  • Extremely high efficiency
  • Low power consumption
  • Easily controllable for intensity and color temperature
  • Extremely long life (50,000 hours)
  • No heat radiated directly into the tank
  • Higher complexity
  • High upfront cost


If I can use all types of blues in my fixture and still grow corals, why is there white lamps? -
Just saying "blue lamp" is a little ambiguous. There are blue actinic bulbs, and there are blue, or high kelvin daylight bulbs. Big difference between the two. A blue actinic bulb is typically just for color, although it does add some PAR. "Blue" daylight bulbs, like the ATI Blue+ are really just high kelvin whites, but they have properties similar to the blue actinics. They have a lot of blue output, which helps with fluorescence, but the PAR levels are much higher than a typical actinic. These bulbs have come into existance because of the average aquirists love of blue looking tanks.

What does T5 mean? -
T5 designates that the bulb is a tube (the "T" part), and 5/8" ("5" eighths of an inch) in diameter. This is a common way to describe a lot of different bulbs. T12s are 12/8" (1-1/2") in diameter. PAR lamps are the same way, but PAR stands for Parabolic Aluminized Reflector. On a PAR38, it means 38/8" (4.75") diameter.

If CF's are no good (according to the census) why in the reef keeping world do they still make them? -
They are cheap, and still come in sizes that T5's don't. Now, not all PCs are created equal. The vast majority are so-so at best in terms of output and color. Newer bulbs like the UVL PC-Rs are much better than your run of the mill Coralife. They use better phosphor blends that increase output, offer better color, and longer life. They still have their limitations, but really aren't built much different than T5s. The big shortcoming with PCs is their shape. Having a pair of tubes side by side causes what's called restrike. What that means is that light emitting from the top side of the bulb hits the reflector and is reflected back onto the bulb, and not into the tank. That light is lost, or at the very least, much less effective. UVL tried to combat that by actually integrating the reflector into the bulb itself, preventing light from actually being emitted from the top side of the bulb.

On the box of a new bulb it shows a chart with color spikes. What is this showing me? -
That is the spectral plot of the bulb. It will give you an idea as to what wavelengths of light are being emitted, and at what relative intensity. To most people, it doesn't mean a whole lot. As you start to understand more about light and what our corals need, you can start to gleen information from that chart, and get a basic idea as to how beneficial the lamp can actually be.

What should I be looking for when it comes to the best bulbs? -
High output, good color, and long life. Most of this has been tried and tested, so you can easily find out what is good/bad/otherwise. Cheap bulbs are typically just that. Cheap.

What is wrong with these lights for reefing or are they for fish only? I'm not looking to buy just to learn.
http://cgi.ebay.com/24-Inch-2x65-Wat...item5191ff2266
Provided that you work within the limits of the lamp, there is nothing wrong with them. You aren't going to be keeping a 24" deep sps dominated tank with those, but you should have good luck with an 18" deep lps/softie tank.