I am tired of everyone talking about how much energy you can save by switching to LED lighting. LED output is well below most long fluorescent tubes is efficiency, and is typically 5 to 10 times the cost. By watt of electricity used, LEDs vary from 15-20 lumens (typical white LED), to 50-60 lumens (most expensive premium LED), which is barely the same as a cheap compact fluorescent bulb. The other side of the story not often told is that high power LEDs generate a lot of heat, and tend to lose efficiency and much of their lifespan by being driven at their rated output. So no, your new overpriced fixture will not save you money over fluorescent lighting, and it will not last for 10 years with no loss of brightness or color shift. LEDs do age, and can vary their color based on output. High pressure sodium is the most efficient lighting generally available (up to 140 lumens/watt), followed by metal halide units (80-120 lumens /watt). A 21 watt t5 tube can have an output as high as 90-95 lumens/watt, much more economical than a 100$ LED fixture with 12 watts at 30 lumens/watt output.
LEDs have several advantages, mostly their package size, durability, and efficiency at LOW power. Most LED fixtures can claim to use much less electricity than your typical 400w halide + 4 55w power compact setups, but they also only put out a tiny fraction of the light.
Summary - If you want a little light to see your fish by, a cheap LED fixture is a great way to go. If you want to grow corals, the high lighting intensity needed means halides or T5 tubes are the best value and still the most efficient. LED technology is still not advanced enough to compete outside of a laboratory.