WHICH TYPE OF COMPACT FLUORESCENT LIGHT TO CHOOSE
For anyone growing cannabis, it is pointless to buy a weak light. Given the option of 8w, 15w and 27w, you would be stupid not to buy the 27watt, as they are more or less the same price. Compare the lumen output of each of the bulbs, different 27w bulbs may have different lumen outputs (depending on the manufacturer) and as with everything, the more lumens the better. You will also be given 2 options, the screw method of fitting, or the bayonet method (push and turn). My preference is the bayonet fitting. Make sure that you choose the right one for your socket! Also, do not choose a regular compact fluoro. Pick the one with the energy saving feature (will be explained why later on in the document). Now, for vegetative growth you should choose the 'cool white' light. This is also acceptable for flowering, but a 'warm white' light will be better as it is stronger in the red end of the light spectrum which is more suitable for flowering.
HOW MUCH LIGHT DO I NEED TO VEG CANNABIS PROPERLY?
It all depends on what light you are using, if it’s HID, standard fluoro or compact fluoro (I assume you're not using halogens!). For HID (HPS or MH) lighting, use roughly 30w per square foot, and for flowering use around 60w per square foot. This is merely a guide, your plant, light height; reflective surfaces etc make a huge difference on these numbers. For a small plant, below 1ft tall, I’d say you would need at least 25w of fluorescent light. I find that it isn't at all practical to use tube fluoro’s for the vegetative stage past 6 inches, as only the top of the plant is receiving enough light to carry out photosynthesis properly.
Using an energy saving compact fluoro will help 'push' the light to the base of the plant, assisting photosynthesis. If the plant indicates it needs more light by growing slowly, and with small leaf petioles, you may need more light. Go with the basic rule of keeping the fluoro’s very close, and using roughly 20-30w per square foot for strong vegetative growth. If you can afford to over-light your grow room, why not? You wont regret it when your plant is bushy and healthy. If you feel that you need to only purchase a minimum amount of lights, you probably shouldn’t be growing.
Growing takes effort and money, and if you can't support a plants needs you might as well just forget growing until you can afford a proper setup. Skimping on lights is the biggest mistake a grower can make, because photosynthesis is so important to for a health plant.
HANGING YOUR LIGHTS OVER YOUR PLANTS
Keep these lights under a reflector all of the time to concentrate the light onto the plant. Hang them horizontally, as most of the light is given off by the middle of the tubes. Keep them close to the plants. As a general rule of thumb, 1 inch away from the top of the plant is perfect. Any more, and you're wasting your time, and less and you risk burning your plant (although these lights are very cool, it is possible to burn your plant if it touches the light or ballast for an extended period of time). If you're given the option, go for a few compact fluoro’s positioned around the plant, as opposed to 1 strong light at the top. Positioning lights around the plant help stop vertical stretching, and encourage the plant to bush out.