This is my DIY on how to build a LED lighting system from start to finish. This design was based on a thread started by SoundWave on reef central and is very similar to his design. This system is based on a modular design with each module designed to be superior to a 250 watt metal halide lamp. The idea being that you use 1 controller, 1 power supply, and as many modules as you need to light your tank. If you don't want to bother with a controller, you can instead simply use potentiometers to adjust the LED output. This article covers construction of the lights. For construction of the reef controller, see DIY Reef Controller
 Parts List For My Module
For the power supply we need to provide 24V to drive the LED's and 12V to drive the micro controller and fans. I'd like to find a reliable and inexpensive part that will handle this requirement but I settled for a 12.5 Amp 24V power supply and a 24VDC to 12VDC converter. Honestly, I'd like to have found a power supply a little bigger than 12.5 amps. The LED's and drivers will use 12 Amps and the .5 amps remaining isn't much head room to drive the fans and micro controller.
By themselves, these LED's throw light out over a 90 degree arc which is going to put most of their output on your walls instead of on your corals. I purchased 40 degree optics, which means the light on the bottom of my tank is going to be about twice as strong. I used a little trig to calculate that with these optics each LED is going to put out a cone about 2' in diameter on the sand bed. My lights are going to be hung about 8" above the water, and my tank is about 2'2" from the top of the sand bed to the water line. If you want to hang your lights higher than me, you may want to check out the 25 degree lenses. They throw a pattern 14" in diameter which was too small for me... But if the light is higher, the pattern will get bigger.
The formula I used:
2 * h * Tan(o/2) = p
Where h is the height of the led above the sand bed, o is the degree of the optics, and p is the diameter of the pattern. So a 34 inch height using 40 degree optics will result in a pattern 27.4 inches in diameter on the sand. Please also keep in mind that for 40 degree optics, this refers to the number of degrees at which the light output is half of it's maximum, so these optics do still spill substantial amounts of light outside this pattern. Also, something called Snell's Law should tighten this pattern up, but I don't know by how much, or if it's significant.
 Power Supplies
Each module runs at 24 V and uses 4 amps of power. I will be creating 3 modules, so I will need a power supply that does 24V and 12 amps. When scaling the system up, you increase the number of amps but the voltage stays the same. You can also use multiple power supplies or even one power supply per module. Having a supply rated for too many amps isn't a problem, but too few will cause the power supply to fail. The voltage should be 24V, but a power supply with adjustable voltage may be usefull... If you find that your buckpucks aren't putting out 1 amp at full power you can adjust the power supply a little higher to give them the voltage they need.
 Possible Design Improvements