i believe a 120W CFL would put out significantly more lumens than 4 x 40W tubes, but the light would be less evenly distributed since it is coming from a smaller, more focused source. of course, that might not be a bad thing if you are growing a variety of plants with different light requirements.

Make sure you're talking about 120W CFL bulbs and not 120W EQUIVALENT bulbs. A 120W CFL bulb is probably over a foot long and will cost over $30. A 120W equivalent bulb is 42W or less and is much smaller and inexpensive.

It's a confusing marketing technique employed by the light manufacturers.

Sam

You could also switch to a T8 setup...I love mine compared to the T12 i was using before...T8 would use less power (32watts?) versus the T12...if you have the cash, CFL's would probably really put out some lumens, but they are costly...