Most specialists will probably agree that your two main options should be fluorescent and high intensity discharge lamps, but you really should give each type of hydroponics light a detailed look before rushing in for a decision.
Superman or Spiderman? McDonalds or Burger King? Friends or Seinfeld? Our life is pretty much a string of these very tough, close-call choices and don't think you're off the hook if just because you picked hydroponics, a field that is new enough not to have any traditional hard decisions.
Still, one aspect of hydroponic systems is becoming hotter and hotter, namely the light source you should use to shine over your plants. Obviously, there are a lot of choices, but in the end, the most popular types of hydroponics lights are fluorescent ones and high intensity discharge (HID) lamps.
I recommend you buy your lamps from a trusted hydroponics store that offers a large variety of lightning products, cheap to expensive.
First off, I'm going to introduce you in both of these concepts, then I'm going to try and figure out a few pros and cons for each.
Fluorescent lights were often deemed the poor hydroponics gardener's choice, but in truth, advancements have been made in the field and nowadays, fluorescent hydroponics lights are competitive and some prefer them to HID lights for efficiency reasons, not just for their lower costs.
Fluorescent lights can be split up into two categories, namely standard lights and CFL's, or compact fluorescent lamps. They both use mercury and argon as a source to power the light, but they only need a small internal pressure to operate, which gives them a lot of advantages (we'll see them in a bit).
Here's a detailed view on what fluorescent hydroponics lights are all about and an introduction to the apparent pros and cons of each choice in your setup.
HID lights are pretty much considered top of the trade right now. A few advantages of Metal Halide Lamps is that they offer the most intense shine and the widest range of spectrum color temperatures. Working on an immense internal high pressure, HID lights generate a lot of heat and consume large amounts of power.
Generally, the best HID's are preferred in larger areas, where more intensity is needed, although they work equally well in close quarters.