It's not that they don't have the right spectrum, it's that most CFL's are low in watts. The 2700K "warm" bulbs do have the proper color spectrum for flowering, but as dutch.lover points out, the more wattage the better. Actually it's not really the wattage, it's the lumens. But usually more wattage brings more lumens. So if you had plenty of flourescents to flower your plant, I think you plant would do fine. I only use CFL's the first couple of weeks and then I put them under stronger lighting.