Ballasts consume, transform, and control electrical power for electric-discharge lamps, providing the necessary circuit conditions for starting and operating them. Electric-discharge lamps include fluorescent, high-intensity discharge, and low-pressure sodium.

  • When comparing ballasts, it's important to understand the following performance characteristics:
  • Ballast Factor (BF) - the ratio of the light output of a lamp or lamps operated by a specific ballast to the light output of the same lamp(s) operated by a reference ballast. It can be used to calculate the actual light output of a specific lamp-ballast combination. BF is typically different for each lamp type. Ballasts with extremely high BFs could reduce lamp life and accelerate lumen deficiency because of high lamp current. Extremely low BFs also could reduce lamp life because they reduce lamp current.

  • Ballast Efficacy Factor (BEF) - the ratio of ballast factor (as a percentage) to power (in watts). BEF comparisons should be made only among ballasts operating the same type and number of lamps.

  • System Efficacy - the ratio of the light output to the power, measured in lumens per watt (LPW), for a particular lamp ballast system.

Also, you might want to select a ballast that bears a seal from the Certified Ballast Manufacturers (CBM) Association. To bear a CBM seal, a ballast must meet or exceed requirements specified by the American National Standards Institute and meet safety standards defined by Underwriters Laboratories. Then there's the "Circle E" label. This label indicates that the BEF complies with the National Appliance Energy Conservation Act.

  • There are three basic types of ballasts:
  • Magnetic Ballasts

  • Hybrid Ballasts

  • Electronic Ballasts.

Magnetic Ballasts: Magnetic ballasts contain a magnetic core of several laminated steel plates wrapped with copper windings. These ballasts operate lamps at line frequency (60 hertz in North America). Of all ballasts, magnetic ones are the least expensive and also the least efficient. They have greater power losses than electronic ballasts. But magnetic ballasts manufactured today are 10% more efficient than the older high-loss magnetic ballasts, which used aluminum windings. Magnetic ballasts are available with dimming capability. However, they can't be dimmed below 20% and still use more electricity than electronic ballasts.

Hybrid Ballasts: Hybrid ballasts, also called cathode-disconnect ballasts, use a magnetic core-and-coil transformer and an electronic switch for the electrode heating circuit. Like magnetic ballasts, they operate lamps at line frequency (60 hertz in North America). After they start the lamp, these ballasts disconnect the electrode-heating circuit. Hybrid ballasts cost more than magnetic ballasts, but they are more energy efficient.

Electronic Ballasts: In the early 1980s, manufacturers began to replace the core-and-coil transformer with solid-state, electronic components that could operate lamps at 20-60 kilohertz. These electronic ballasts experience half the power loss of magnetic ballasts. Also lamp efficacy increases by approximately 10% to 15% compared to 60-hertz operation. Electronic ballasts are the most expensive, but they're also the most efficient. Operating lamps with electronic ballasts reduces electricity use by 10% to 15% over magnetic ballasts for the same light output. They're also quieter, lighter, and they virtually eliminate lamp flicker. Electronic ballasts are also available as dimming ballasts. These ballasts allow the light level to be controlled between 1% and 100%.

There are a variety of electronic ballasts available for use with fluorescent lamps. Electronic ballasts have been successfully used with lower watt high-intensity discharge (HID) lamps (primarily 35-100W MH). These ballasts provide an energy savings over magnetic ballasts of 8% to 20%. Their lighter weight also helps in some HID applications, such as track lighting.

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