Fluorescents come in a wide variety of shapes and sizes. There are compacts, twist bulbs and circle bulbs. They all work the same way. They have a starter and ballast which help provide a steady and regulated amount of electricity to the light. Before HID lights were available indoor growers used fluorescent lights. While fluorescents can be used for an entire grow from seedling to harvest, it is generally not advised to use them in this way. To grow effectively with fluorescent's, think small. These lights are better suited for starting seedlings, rooting clones and small plants, maintaining moms for cloning purposes, and providing sidelight for the undergrowth. These situations do not require a high intensity of light to run their course. The light emitted by fluorescents is gentler and more diffuse, it doesn't release a lot of heat, and doesn't make the plant work as hard. For this reason they can be kept closer to the plant. One or two inches is sufficient, but this also means that the lights must be adjusted almost daily to accommodate growth which can be troublesome.
HPS lights are the best light available today for growing marijuana(The flowering phase). High pressure sodium lights are very bright and very efficient. HPS comes in a wide variety of wattages from 70 watts up to 1,000 watts. With enough of these kind of lights you too can grow those centerfold buds. Even BabyGro will back this up!
You'll never get the ultimate perfection you get with HPS with fluorescents, because they simply do not output a sufficient volume of lumens or the small amounts of UVB radiation you get with HPS systems that produce those hard dense nugs, but for people on a budget, working in small enclosed spaces, growing a couple of plants - fluorescents in all their guises offer a very real and a very viable alternative.