Lumen output is only part of the story. Is the hps air cooled? That glass takes out 10%+. Do you have your one light 3 feet above the highest part of your unkept canopy? (I Don't mean you, just hypothetical )
You get were I am going though right? I think equal would come out fairly equal if you do a banging job!

To the original poster: If you have everything dialed in, and are efficiently using 10000 lumens per square foot, you shouldn't have a longer harvest period. That would assume shorties or SCROG though. Otherwise, the plant will get weird if you let them get very tall or very far away from bulb.
2"-4" max. Oh, that's a lot of Cfl's per square foot though. 7 23 watters of the "bright white" I just saw would be 105000 lumens. That's a lot of bulbs in a small spot. So realistically, you will probably use less, and it will take a little longer. But with time, ingenuity, and good venting, you could do it. imo

Quote Originally Posted by Italiano715
When using CFL's it doesn't have the same lumen output as a HPS, so you would virtually have to use more wattage from the CFL's.

Basically 250W of CFLs is not the same as 250W HPS...The HPS has a lot more lumen output then the CFLs, plus the HPS penetrates further into the canopy usually resulting in bigger buds, I.E. all other conditions are met.