I see the question asked so much here and I see it answered incorrectly just as much. LISTEN UP: THE ONE AND ONLY CONTRIBUTING FACTOR TO HOW POTENT YOUR BUD TURNS OUT ARE YOUR PLANTS GENETICS. PERIOD. QUANTITY: More light, bigger pots, perfect growing conditions(temp, nutrients, light cycle, air quality, use of light(reflectors) These are the things you need to be concerned about if you are after QUANTITY The rest is really down to genetics and technique. QUALITY(for the sake of this article I am using quality to term the physical nature of the bud): I have seen FAT, DENSE buds come from cfl grows. I have seen STRETCHED, AIRY buds come from 1000watt hps grows. It still has a ton to do with technique and a ton to do with genetics. "I'm thinking about growing. Should I get cfl's or an hps? What's the difference?" Here's the REAL difference. A 400 watt HPS bulb penetrates like a porn star. Put your plant in a pot, water, harvest, smoke. Does that mean it's the best route to take? Not necessarily. If you are going to use CFL lighting then you need to be ready to work for it. Ideally you will need to use LST at least and a SCROG at best. This allows you to cover more bud sites with more light therefore evening the odds with those HPS grows. You can still let them grow naturally but you will have to use your lighting in a more creative way(placing many bulbs all around the plant to give the best coverage possible. EITHER WAY YOU DECIDE TO DO IT, THE POTENCY OF YOUR WEED WILL STILL BE THE SAME. IF YOU SMOKE A 1 GRAM JOINT OF WEED GROWN UNDER HPS, OR IF YOU SMOKE A 1 GRAM JOINT OF THE SAME WEED GROWN UNDER CFL, YOU WILL BE SMOKING THE SAME AMOUNT OF THC, CBD, KFC, PCP, AND MF-E.T. I'm not hating on anyone in particular, or anyone for that matter. I just want people who are stepping into the world of growing to stop being so intimidated to do one versus the other. Not everyone is trying to do some big 5lb yield commercial grow so let's stop being so aggressive when pushing people to choose their lighting. Give your plants some light and smoke the results. Isn't that what we all want anyways?