pg14
led info
The current through an LED is established by the voltage drop across it. But here is the tricky part.. the relationship is not a predictable constant and it is not a linear relationship. The voltage drop required to produce the desired current will vary from LED to LED even in the same bin. It will also change with operating temperature and age of the LED.

I have been designing,hand building and using high power LEDs to grow for almost a year. When I build an array, I burn it in for two weeks powering it by a bench constant current power supply. I then measure each series string and set the current limiting resistor (or LM-type regulator) to the exact value needed for that string.

Another tip: If you are trying to achieve energy efficiency you should be driving them at 350 ma instead of 700 ma. If you are trying to get the most light output for your money, then go the 700 ma. The high end commericial lights all drive at 700 ma in order to cut material costs. If you double up on LEDS used, drive at 350 ma, you will pick up about 20% better energy conversion efficiency. Plus you will have twice as many points of light.

I ordered up 20 of the Ledengin 660s to integrate into my setup as soon as I can find the time. I will only be using them on a portion of the crop so I can get an idea of the difference if any. I will be removing an equal wattage of 630s to get a fair comparison.

If you are trying to pick up some 660 energy,you might also try using the K2s instead of Crees for your 630s. They have a much wider bandwidth and only have about a 60%-70% drop from peak at 660. Looking at the SPD charts, the Crees ain't got nothin at 660. Also you might try using warm whites since most of them put out ok power at 660. Probably the best one at this time is the SSC P4, but the K2s aren't bad.
pg15
Thanks for the links, found some really useful info.
If you want to build your own drivers, you got to check out National Semiconductor, High-Performance Analog for Energy-Efficient PowerWise Designs. They got some really slick design tools, you can even order up a prototype kit for your design.

i-- let me know what you want to do. I can help you with any electronic design issues and step by step construction (with pics) and parts sourcing.

I got lots of practical hands-on experience and have done mucho research. The 24 volt drivers used in the sign and lighting industry are a good way to go but can get a bit pricey.

I am not much of a computer guy, but I heard somewhere that some of the older Macs had a 24 volt 3 amp source on their power supply. Anybody got any info on this?

I took the time to read your post a little bit closer.
If you mean the "Advanced Transformer" 60 watt Xitanium driver, that is a very good choice.
I strongly recommend running the LEDs at 3 watt instead of 5. You will get better energy efficiency, longer life, and your thermal issues will be much easier to deal with. 1 watt would be optimal, but those little buggers are just to damn expensive to run at that power level. I personally run the 660nm LEDengins at around 3 watts.
First, you are going to need 9 square inches per watt of heat sink exposure to air. 36 watts is going to need 324 square inches. You count both sides of all the fins and top and bottom of platform when making this calculation.
There is a guy on ebay that sells them cut to your size at very reasonable prices. I would go with about a 4.5 "x 12" and use a to a couple of computer fans on top.
Unless you want to order in another 4 LEDs, which would be a better choice, you are stuck at running 12 volt instead of 24. If running 12 volt, just buy a PC power supply for $10 to $20 bucks. Assuming 2.9 volt drop for 1 amp of current, you will need to run 3 parallel chains of 4 LEDs. You will want to use a .4 ohm resistor in each leg with minimum 2 watt minimum rating.
If I was only running 12 LEDs, I would consider making 3 small units instead of one, so I could be more flexible where I put the light