Fluorescent Lamps:
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A ballast basically consists of an electric or electronic circuit that regulates the current (limits it) so the discharge stays in control. The ballast also provides the proper voltage to start and operate the lamp. One end of the ballast connects to the electrical line, the other end to the lamp it operates.

Ballast used to be magnetic (or “electromagnetic”) and contained coils, transformers etc.. Today lamps are mostly operated on electronic ballasts. These are (1) lighter weight and smaller size (2) increase system efficiency because they dissipate less power themselves and manage to squeeze out more light from the discharge (3) operate at very high frequencies (typically 20,000 cycles per second and more) thereby eliminating strobe and ballast hum.

Further, ballasts can be Rapid Start or Instant Start.