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Shedding Light on Ballasts

Key Points
  • Light ballasts provide a boost in starting voltage and regulate electric current during operation.
  • Different types of ballasts are available, each with their own advantages and disadvantages.
  • Ballast factor determines total light output and can impact energy use and lighting system design.

Source: http://www.lbl.gov/
Ballast
When it comes to lighting systems, most of the attention is typically focused on lamps. While lamp efficiency and technology is important, ballasts are equally critical in lighting operation. Understanding how ballasts work and the different types that are available is important when designing an efficient lighting system for your facility.

What Are Ballasts?

Ballasts are used in fluorescent and high-intensity discharge (HID) lights to provide proper starting and operation. When starting, most fluorescent and HID lights require a voltage several times higher than line voltage to create an electron emission or arc. The voltage available in most facilities is not sufficient to do this, so ballasts were developed to provide the needed starting voltage. The electron emission or arc generated in a lamp has almost no electrical resistance, so the ballast is then needed to regulate the current once the lamp is in operation.

Ballasts are typically magnetic or electronic in design, with electronic ballasts using high-frequency waveforms (>20,000 Hz) from solid-state circuitry to achieve higher efficiency operation than line frequency waveforms (60 Hz) from a magnetic coil. Electronic ballasts not only have reduced heat losses, but they also improve the efficacy of the lamp-ballast system by up to 20%. Magnetic ballasts are still used in older T12 fluorescent lights; however, more efficient T8 and T5 lamps use only electronic ballasts.  

Magnetic ballasts for fluorescent lamps are no longer available for sale in the United States, due to federal energy-efficiency regulations that went into effect in 2010. The regulations require that all currently manufactured commercial and industrial fluorescent luminaires incorporate electronic ballasts. The rules do not require facilities that currently use T12 lights with magnetic ballasts to replace them. However, an upgrade to more efficient lighting technology can help you save significantly on energy costs.    

Types of Ballasts

Ballasts consume energy over and above the lamp watts rating, and ballast type should be carefully considered when evaluating the efficiency of the lamp and ballast system. A number of different options are available, including the following:

  • Instant start. Using a very high voltage, this ballast type starts lamps without heating the electrodes. This is the most energy-efficient option; however, the higher starting voltage can reduce lamp life. Instant start ballasts are a good fit for applications where lamps are not turned on and off frequently.
  • Rapid start. With this type of ballast, the lamp electrodes are heated prior to start, reducing the voltage required. Rapid start ballasts provide longer lamp life, but use slightly more energy than instant start models.
  • Programmed start. An advanced rapid start ballast which applies the starting voltage once the lamp electrodes have reached a precise temperature, helping to extend lamp life. Programmed start ballasts have longer starting times, but are appropriate for use with occupancy sensors or other frequent switching applications.  

Ballast Factor

Ballast factor is an important, but often overlooked element in lighting design. Ballast factor is a measure of how hard a ballast will drive a lamp compared to the lamps rated performance. The ballast factor is derived by dividing the lumen or light output of a specific ballast/lamp combination by that of the same lamp with a reference ballast. Ballast factor is expressed as a percentage figure, ranging from 0.78 to 1.2. Ballast factor is usually fixed for a given ballast, but some ballasts offer multiple settings.

While ballast factor does not directly measure energy efficiency, it can have a significant impact on lighting design or retrofit decisions. By choosing different lamp and ballast combinations, varying light output and energy savings can be obtained. Lower ballast factor generally results in energy savings, but it can reduce light levels drastically. Ballast factor levels should be tailored to the space or application. For example, in new construction, a higher ballast factor can increase light levels and reduce the amount of lighting fixtures. In retrofit situations where light level is not critical, such as a hallway, a lower ballast factor may be more appropriate.

By taking into account different ballast types and performance levels, along with lamp efficiency, lighting requirements and other factors, you can make better decisions about energy-efficient lighting systems for your facility.

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