That looks like a decent light, but it only actually draws about 300 watts at the wall.
http://www.crxsunny.com/product/crxsunny-1800w-cob-led-grow-lights-full-specturm-growing-lamps-for-indoor-plants-veg-and-flower-19.html
With this type of lighting, you want about 50 watts per square foot in flowering. I would recommend about double, maybe even triple that much light for a 4x4. There are several lighting threads. Specifically, check out this one:
Even if you feel like DIY might be too much, there is a ton of info and other links from there. Hope that helps you some! 