Ballasts

Fluorescent and HID lamps require a ballast to apply starting voltage to the lamp and establish current flow—an "arc"—between the lamp electrodes. Once the lamp is operating, the ballast also regulates lamp current and power.

Ballast types fall into two broad categories:

1. Magnetic

   A simple device that uses a core and coil assembly transformer to perform the minimum functions required to start and operate a lamp. Magnetic ballasts are often found in HID systems, as well as older fluorescent systems.

2. Electronic

   A more complex device that substitutes electronic components for the core and coil assemblies found in magnetic ballasts. Electronic ballasts are significantly smaller, lighter and quieter than their magnetic counterparts—and offer distinct advantages in energy efficiency and lamp operation.

   Ballasts, particularly for fluorescent systems, can be further categorized by their lamp starting and operating method. Starting and operating methods now available are balances between lamp life, energy consumption, and overall system costs that allow the user to select the system best suited for their application.

   First introduced in the early 1980s, electronic ballasts are now commonplace in modern fluorescent systems, and will become more prevalent in HID systems. These devices offer many advantages over magnetic ballasts, notably in their smaller size and lighter weight, which allow manufacturers more options in fixture design. Another important feature of electronic ballasts for fluorescent systems is high frequency (= 20kHz) operation, which eliminates the noise and visible flicker associated with magnetic ballasts, and yields approximately 10% more light output than equal wattage magnetic systems. This increased luminous efficacy can then be parlayed into significant energy savings if the user wants to maintain existing light levels.

   Both fluorescent and HID systems can be dimmed for energy savings and/or architectural applications. For example, dimming may be used in daylight harvesting systems to compensate for available natural light. In multi-purpose spaces such as conference rooms and auditoriums, dimming is used to match light levels with the occupants' needs. Electronic ballasts are compatible with 0-10V dimmers, and can operate T8 fluorescent lamps over a wide (100-5%) dimming range. HID lamps can be dimmed to approximately 50%; dimming below this level can result in color shift and shortened lamp life.