OK so you need something like 16ft2 x (40 or 50W/ft2) = 640 to 800 watts and we are talking real watts not theoretical. Coverage is really just about as important as watts (or maybe more important) which is where many people fail. Take the size of the fixture (whatever it is and add about 2 - 6 inches per side...so 4 to 12 inches to the length and width. For example, you seem to like the BD450 which is 16.5 x 16.5 inches. It will effectively cover (at most) about 28.5 x 28.5 inches...so lets round and say 2 ft x 2 ft or 4 square feet. I would bet my paycheck on it not giving good growth over a 3.5 x 3.5 ft2 area.
There are ways to increase the effective coverage of a fixture - use some kind of light mover or spinner. So if put on a 4 ft light mover, you could flower well over about 2 ft (width of fixture coverage) x 4 ft (length of light rail in your tent) = 8ft2.
Here are some ideas to cover your area for your budget.
1.I use Kessil H350s and a spectral spinner....I also use some fluorescent side lighting. It has worked very well...but I think that part of my success with the Kessils is due to 1) the spectral spinner which increases effective coverage as we've discussed and 2) the Kessils are primarily red/blue and the fluorescent white lighting would not only have provided extra light but also a different portion of the spectrum. I don't know how much #2 played but it probably played some. You could get four H350s and a spectral spinner from growershouse.com for your budget. Of course if buying several pieces, try to bargain. The spectral spinner will accommodate up to 6 fixtures so you can easily add more later as desired..to just add light or change spectrum...or..? I (unlike others) actually own and have used these LEDs with good results...not speaking from others posts but my own experience..and grew some incredible bud. I actually had a hash tip on one plant. Woohoo!
2. Hans makes a nice (at least from what I see of the panel and some grows) panel. If you spoke with him and got four panels (in your budget at regular price and I would ask for a discount for buying 4...can't hurt to ask), you should be able to cover your space pretty well. Each panel is 10 x 15 inches so the max effective area is about 22 x 27...so once again let us just round to 2 x 2ft or 4 ft2. With four panels you have covered the space reasonably well. Now I would still put in some fluorescent sidelighting myself as it's cheap, adds light generally and spectrum that may be missing in the panels. The panels are low wattage but the coverage is good; you can keep the panels fairly close to the plant so you can get away with lower watts than when using a more point source oriented LED fixture which needs to be kept further from the plant to attempt to give coverage. This is about as low wattage and thus long-term economical as you can go and grow good bud.
http://www.bonsaihero.com/ledgrow.html
Another manufacturer that seems to have good results from what I've seen is Area51 but they are in between lines so I don't know what they'll have in the future.
You really need to get away from thinking about a point source of light - like with HID. Unlike HID, coverage may be as important as watts with LED so
multiple small fixtures and/or
movement works well. If for some reason (and I don't know why), you want only one panel for your space put it on a light mover.
Oh,and the BD-450 is not 900 watts. Theoretical light doesn't grow plants. Your budget is really just adequate to cover the space. If you try to go too cheap, you will end up unhappy with the results and have wasted your money. Buy quality once and be happy as you smoke the dense, flavored buds. If you end up being unhappy with either the Kessils or the Hans Panels (I really think it's unlikely but..), they are known brands and are rather easily resold for a good percentage of what you paid.
