Help request - total watts for LED array

Basically I'm trying to decide on an appropriate wattage for my grow space. Dimensions: 32"x72" same as: 15 square feet.

The # and model of LEDs I've picked out driven at 65% of max comes to 700 watts almost exactly. Friend suggested I should be closer to 900 watts.

Would there be any benefit to increasing the wattage for the space I have in mind? I don't want an underpowered system, but I was thinking 700 watts would be pretty beefy. Here are some stats.

18 units: Cree CXA-2530
Driven @ 700 watts - 39 watts per sq ft
Driven @ 900 watts - 50 watts per sq ft

I'll be using large passive heat sinks. If I stick with 18 units they would need to be driven at 93% max output to reach 900 watts. There are other options such as adding more units, or seeking out more powerful emitters if I want to keep the same array.

I don't expect anyone to do research for me, but if someone with experience can comment on the wattage distribution and the thermal situation it would be much appreciated.

I wasn't including power loss from the drivers. With that factored in it puts the draw at just over 800 watts pushing the emitters at 65% of max so it looks like I have a plan.

The only other thing I need to consider is the warm/cool ratio. I saw the post on the Cree CXA-3050 100watt 2700K and was impressed at how compact the plant grown under it was. So now I'm wondering if I really need to add any 5000K emitters.

With a room that size, you might want to consider a few panels, instead of just one large one. But 900W total isn't too crazy, imo....I have ~300W on a 1'x2' space.

Thanks for the reply. The panel itself will be 20"x60" and should be around 50lbs. which I can handle. I did consider two panels for convenience but it would increase costs a little bit. As far as the wattage it will be almost exactly 48 watts per foot and that's not including the loss from the drivers. I'm thinking that's going to do a pretty good job.

This sounds a lot like what I have been invisionig. It sounds like you are envisioning a large hanging framework with 3 rows of six lights spaced about 15 inchs? That would evenly space everything, with even light coverage at maybe a foot above the plants(guessing). I assume the frame would also be the heat sink? What do you plan to make it with? Are you doing to have active cooling or do you think the over all mass and distribution will be enough?

I was was just thinking there needed to be a "let's talk about how exactly to build a big ass array now that bbs showed ge level of assume thread".

How do you plan to power the leds? I don't think you need to much "help" I bet you have a spread sheet already!

I am am super interested in this build.

I started with a square grid but switched to a hex. The frame will be made from 1" aluminum tubing found at Lowe's. Aluminum heat sinks will be bolted to the frame. The lights emit at 115 degrees and will be spaced 10" apart so I'm thinking a 12" height will be ideal, allow for light mixing while keeping a tight footprint. It will be passively cooled though I will probably have a couple small fans pulling air above the unit.

Each emitter will have it's own driver and the cobs will be mounted with connectors made specially for them and thermal paste. Everything will be swappable. I'll have a couple extra cobs and drivers around in case something fails.

You can find a smaller version of what I have planned here: http://howtogrowmarijuana.com There are a couple pics showing the heatsink and the final build with everything mounted in the frame.

And here's a fancy pic of the array and the tentative color arrangement.