I set one of these up for approximately a 2'x2' area, though you could go larger depending on the desired light level. The issue with just using one is that it's basically a point-source light so it'll cast strong shadows and won't have as good of coverage as something like a fluorescent light. You can mitigate this somewhat with reflectors, though it may be a better idea to set up more than one LED. The other issue is that LEDs are more efficient the lower the output power, so if you were to set up 2 both running at half the power of one, it would be producing more light, and even more with 4 COBs running at 1/4 the power of one.
I don't know of any way to calculate an exact lumen output since no two LEDs are the same, but I estimated at least 8000 lumens running my LED at 50W - so somewhere around double the efficiency of T5HO fixtures. I don't have the light properly distributed since I don't have any sort of reflector set up so it's a lot stronger in the middle than at the edges, which actually works well for the various types of plants I'm growing. It is strong enough in the middle to turn my supposedly lime green Heliamphora solid red though.
