DIY LED parts list for 6 foot long planted tank

IMO, fans are always a good idea. Heatsinks will pull the heat away from the LED but the heat gets trapped in the fins of the heatsink and acts as a hot blanket if you do not have any airflow over the fins to push the heat away. It takes just a small amount of airflow over the fins to push the hot air away, so you don't need a big/fast/loud fan for the job.

How high off the tank are you planning on mounting the light? That will determine which optics to go with. If your going 20+ plus above the water line, then 40's, if you go 12"-20" go 60's, 4"-12" go with 80's, and if you set the LEDs right above the water line, no optics.

Since this is a planted tank, I think going with XM-Ls is serious overkill. I think you could get by fine with XP-G cool whites in the same number your thinking (36-48). I run 48 on my 75G tank, but it is reef so it needs the extra light, planted tanks do not. They are the "best of the best" today (XM-Ls) but you pay a big premium for them and I don't think you get your moneys worth out of them right now because they are so new and pricey compared to XP-Gs. I think going with just cool whites is fine on a planted tank though, unless you want more yellow/reds in the tank, then maybe put in a few warm whites scattered through out. Any blues though are not needed at all on a planted tank and would probably make it look very weird and unnatural so it is good to see you didn't even consider that for your tank.

For general comparison, I think 9w of LEDs (3x 3w cool whites) is equal to the output of a 65w CFL 10k bulb as far as the plants are concerned. I think it takes about 9 LEDs (27w) to equal the output of a 54w 4' T5HO 10k bulb. Just a general comparison since it is a little hard to compare such different styles of lighting (small intense points of light vs long tube of light).

I know it cost more money up front, but going with dimmable drivers and a dimmer kit really is worth it since you can "fine tune" the output of the LEDs. If you go with a constant current driver like you mentioned (I use those on my sump) and the light ends up being to strong for the plants there isn't much you can do except take the light down and remove some LEDs. With dimmers, just turn a knob slightly and all set. I would not build a display LED light without dimming capabilites myself, especially after building a few and seeing how I went way overkill on my builds (I had them turned up 3/4 of the way, so 750ma on my reef tank, and nuked my corals from too much light when I initially installed it).

IMHO, the heatsinks are a little overkill. You can screw the LEDs onto a sheet of aluminum or something and it will cool them down sufficiently. That, or if it doesn't, you can always mount little active heatsinks onto the aluminum sheet.

If you were talking about 1w LEDs, then an aluminum sheet may be sufficient to cool them, but when you get into 3w LEDs there is no way that would suffice. Even a good heatsink with fins is no were near enough to cool 3w LEDs without a fan (I used a 23"x4.5" heatsink on 24 LEDs on my 29G tank and you would burn your fingers if you touched the heatsink after 30 minutes of use without fans on it).

As far as mounting, the thermal epoxy is probably the best, cheapest, and easiest method to mount them. I used the thermal pads but they are expensive and I don't think they work as well as epoxy (LEDs don't stick as well). Screws work but that is a big pain in the butt drilling and tapping that many holes.

If you have previous Arduino experience and feel comfortable with it then the Reef Angel is a great product.. for the masses though that are afraid of programming I would probably recommend something else like the Apex Jr instead (you can do dimming control with any modern controller, Adruino needs the -P version of drivers, the Digital Aquatics and Neptune controllers can dim the -D models).

Yes, for 4-6" above the tank I would recommend 80s, anything tighter than that at that distance is going to give very noticeable light bars in the water. I recommend starting on the low side of the amount of LEDs you think you will need and add more if you think you need them, vs the route I went, which is put 2x as many LEDs as I found out I actually needed because they are much stronger than I thought before I started building them. I probably wasted $300-$400 on my original build because I went way overboard. If you got the $, nothing wrong with that because you just turn them all down and they will last a lot longer, but the reality is, if they last 5 years at full power or 10 years at 1/2 power, I will more than likely be replacing all my LEDs in 5 years anyway because there will be MUCH better LEDs on the market at that time and probably cheaper than what I paid today.

i dont think 80 deg optics exist for the xm-l, and the optic for the xp-e is not going to fit, optics are an easy addition however
what is your source for the leds?
ledgroupbuy.com is pretty cheap and the t5 bin (which is enough for you) is going to be enough, but if the xp-g is any cheaper you might as well do that since at 700ma the output is going to be about the same, you dont see much benefit between the xp-g and the xm-l until you get over 1000ma at least iirc

another way to cut down on cost is to get bigger leds, like bridgelux (which you definateley want to drill and tap for) and use less of them, either that or get higher powered drivers, and continue to use the xm-l, raise the array and increase the current, at 2000ma its still very effecient and will still blow any other light source out of the water

Forgot to touch on one point that you mentioned.. "I really worry about not having enough lights, because to get the nice red plant colors, the extra light really comes in handy."

I bet putting in a few of these would really help both the "red plant colors" and overall usable light for the plants since they are 660nm, perfect wavelength for plants. I would guess 6 on your tank, 1 every 12". Then put in a similar amount of warm whites, so one driver will have both the reds and warm whites on them which you can dim separately and give you some control over color of the tank. Put optics on the warm whites but the reds do not need optics since your using them to add color to the tank, you want the color to spread out as much as possible.

http://www.rapidled.com/servlet/the-172/Osram-660nm-3W-Red/Detail