Fluorescent tube grow lights come in 3 different diameter bulbs, T12, T8, and high output T5. T12 are the most common ones you see used at the store for lighting. They are the cheapest but do not produce a very bright light but they are great for starting seedlings or clones. T8 grow lights are a bit better and can actually be used to grow lettuce or basil and other less demanding plants. T8 bulbs can be rewired and overdriven to produce almost twice as much light out of each bulb. I made a video that shows how to overdrive a fixture which I'll post at the bottom of this page.
Here to the left you can see Radish plants ready to harvest the I grew under two T5 bulbs. These plants are only 25 days old from seed and you can see how well they did. T5 fixtures and bulbs are rather expensive but the do a great job. I have seen people grow tomatoes all the way to fruit under a 4 bulb T5 fixture. If you are looking for a fluorescent grow light I suggest getting T5.
I keep the fluorescent grow lights 1 to four inches above the tops of the plants. The bulbs give off very little heat. Even if the leaves touch the bulbs they will not be damaged too much.
You can rewire a T8 fixture and add an extra ballast to the fixture to give more power to each bulb. A normal 2 bulb fixture has a sigle ballast powering 2 bulbs. An overdriven T8 fixture has a single ballast for each bulb giving it almost twice the power. The light output is close to that of a T5 bulb which will save you money if your willing to do the work to create one. I bought a couple of very cheap T8 fixtures at Wallymart and combined them to make an overdriven fixture. I'm not sure if this works with older magnetic ballasts but I do know it works with the newer electronic ballasts. Be sure the fixture you buy has electronic ballasts Below is the video I made which shows you step by step on how to do that.