Quote Originally Posted by jamstigator
Not much light at the edges of a 10'x10' room with just one 1k light. I use a 1k light in a 4'x4' hydrohut, and that seems about right, maybe a tad overkill. That comes out to about 60-ish watts of light power per square foot, so just a little more than the optimal 50. I could cover more area, but I'd have to raise the light significantly to do it, which would increase the distance between the light and the plants. And light intensity doesn't diminish linearly with distance, it's much worse than that. Let's say you're generating X lumens/sqft at 1 foot distance. At 2 feet, it's half that. At 3 feet it's 1/4 of that, at 4 feet it's 1/8 of that, and at 5 feet (the center of a 10'x10' room to the edges) it's 1/16 of the light intensity that exists at 1 foot from the light.

The general rule of thumb is: 400 watt HPS light = 3'x3' square. 600 watt light = 4'x4' square, and 1k light = 5'x5' square. Thus, a 10'x10' room would, realistically, need four 1k lights, if you used the entire space for flowering, and wanted reasonable yield from all of the plants. If you don't care about yield, then sure, you could use one 23-watt CFL in a 50'x50' room. Just wouldn't get much from each plant.
This is pretty much right on. The 400=3x3 and 1k=5x5 room is pretty much the max that those lights can handle efficiently.