The above image of a fluorescent tube fixture is from Full Bloom Hydroponics.
Welcome to our page about fluorescent lighting. While fluorescent tube lighting is now extremely commonplace, it also has specific applications for starting and growing seedlings. Let's take a look at where they work, and where they may not be the best option.
Most hydroponics and aquaponics books no longer list these fixtures as growing area options. Strictly speaking, they don't even qualify as being HID light sources. But they are so commonly available that many people stil use them. For that reason alone I've included them in this HID lighting comparison.
Fluorescent tubes are extremely common, relatively cheap, moderately long-lived lighting fixtures which seem a natural solution for folks just getting into indoor plant production. Aside from the advantages already mentioned, they are available in a wide range of spectrums, from cool white to full spectrum to plant-growth stimulating wavelengths. The tubes are fragile in and of themselves but the fixtures can be nearly bombproof if you need them to be, and the fixtures almost always have built-in ballasts. They do not put off any detectable heat so they can be located immediately next to even tender young seedlings without damage. And the fixtures are lightweight enough that they can be hung from a wide variety of homemade supports, and easily raised or lowered according to the plants' requirements. Best of all, if a tube breaks, the replacement tube is as convenient as visiting the nearest hardware store.
Unfortunately, fluorescents have some serious disadvantages. First, they do not actually put out a lot of light compared to other grow lights. Any room with ceiling heights much beyond 8' needs to have nearly continuous fluorescent tube coverage to provide for anything close to the amount of brightness really needed by plants. Anything less than that will result in leggy growth which will fall over, wilt or simply burn up once subjected to natural sunlight. If plants are allowed to mature under fluorescent tubes, they may never reach maturity but simply grow ever more spindly and pathetic, eventually dying of light starvation.
Secondly, these fixtures may be more energy-efficient than incandescent bulbs, but they are far inferior to modern HID lights such as metal halide and high pressure sodium. That's because they put out so few lumens compared to their wattage. A single 4' long, two-tube fluorescent fixture may be rated at 100w, won't put out enough light to keep a single tray of lettuce plants happy for very long. Replace that fixture with a 100w metal halide light fixture, and your lettuce will grow very nicely. Same power requirements for both, but the metal halide puts out much, much more light.
Yet these bulbs have a solid place with seedling development precisely because they provide low heat, good light coverage (even if it is at relatively low levels) and relatively lightweight fixtures. And conveniently a 4' shop light just perfectly fits over a bench with four trays. Put that shop light on chains so that you can raise it one or two links per day, and your plants will get off to a better start than if you had used a single metal halide far above them. If for no other purpose, seedling starts will probably continue to favor fluorescent bulb fixtures for some time to come.
Fluorescent lighting has been around for several decades now, and a wide variety of configurations are very easy to find. Most hardware stores, home improvement stores and industrial supply houses will carry them. If you only need one or two fixtures, your nearest hardware store would probably be the simplest way to buy them.
Specialty hydroponics and general commercial nursery or greenhouse equipment suppliers may very well not sell these fixtures for two reasons. First, these fixtures are no longer considered a good solution for most growing circumstances, so these specialty suppliers wouldn't sell many of them. Secondly, the big-box home improvement stores go through so many of them that they can stock them at much lower prices. So that would be your best bet. One example can be seen at Home Depot's website, which lists a wide range of fluorescent tube fixtures.