To flower properly, you need to reach over 5000 lumens a square foot, closer to 10,000 a square foot is better. Say your grow space is tiny, 2x2. You need 20,000 lumens minimum to flower a good yield. A 42 watt CFL gives off 27oo lumens. You would need 7-8 of them to reach the desired lumens/sq ft ratio. 7x42 = 294 watts. And you would have spent around 8 dollars a piece for those bulbs. All of that said, a 250 watt HPS would both save you money in energy, be VERY close to the cost of the CFLs, and give you nearly 50% more light, while using 50 less watts. And it would undoubtedly run cooler than 7 42w CFL's. Just saying, I used to be a CFL guy too, but just recently made the switch, and DAMN.