Two general types of fluorescent lamps are available. The
traditional tube-type fluorescent is usually identified as T12 or
T8 (12/8 or 8/8 of an inch tube diameter, respectively) and is
installed in a dedicated fixture with a built-in ballast. The newer
compact fluorescent lamps (CFLs) and circulines have smaller
diameters and are usually bent or twisted into compact shapes.
These are frequently sold with built-in or separate electronic
ballasts and screw thread adapters for application in fixtures
designed for incandescent bulbs. Dedicated fixtures that are
equipped with electronic ballasts and that use plug-in (pin)
CFLs are also available.