Howdy Giannhs, I have been growing with CFLs for the last ten grows, I use a total of 220 watts per planter (Bubble Phonics style) consisting of two 55 watt lamps at 2700° K and two 55 watt lamps at 5000° K. I have been using the 'rule of thumb' of keeping the lamps as far (or close) to the plants as I can keep the back of my hand. If it is too hot to keep my hand under the lamps, then it is too close for the plants. The only time that I keep the lamps farther away (about 8 inches or 200 mm) is during the early seedling growth stage.