I found out the hard way. When I placed my gals into flowering stage, they actually grew an additional 2/3rds more. I had to move stuff around to make more growing space. I placed my cfls on top, along the sides, everywhere.
I used eight 105watt/400watt, 2700k, 5000 lumen and two 85watt/350watt, 6000k, 4500 lumen, during the flowering stage. You can mix up your CFLs as long as you do not exceed over 50%, example 4 cfls @ 2700k, but no more than 2 cfls @ 6000k. Many growers are stuck on hps hid lights, but I'm sold on CFL grow lights. With CFLs, heat is not an issue and using clamp fixtures you can place light anywhere to serve your plants. Good luck on your grow.