Lighting Research Center Lighting Research Center
    Volume 7 Issue 4
June 2003    
ballast - A device required by electric-discharge light sources such as fluorescent or HID lamps to regulate voltage and current supplied to the lamp during start and throughout operation. ballast factor (BF) - The ratio of the light output of a fluorescent lamp or lamps operated on a ballast to the light output of the lamp(s) operated on a standard (reference) ballast. Ballast factor depends on both the ballast and the lamp type; a single ballast can have several ballast factors depending on lamp type. compact fluorescent lamp (CFL) - A family of single-ended fluorescent-discharge light sources with small-diameter [16-millimeter (5/8-inch) or less] tubes. electrodes - The structure that serves as the electric terminals at each end of electric discharge lamps. high-intensity discharge (HID) - An electric lamp that produces light directly from an arc discharge under high pressure. Metal halide, high-pressure sodium, and mercury vapor are types of HID lamps. luminaire - A complete lighting unit consisting of a lamp or lamps and the parts designed to distribute the light, to position and protect the lamp(s), and to connect the lamp(s) to the power supply. (Also referred to as fixture.) load shedding - The practice of turning off electrical devices during peak energy demand hours to reduce building energy use. rated lamp life - The number of hours at which half of a group of product samples fail. The rated life is a median value of life expectancy; any lamp or group of lamps may vary from the published rated life. Rated life is based on standard test conditions. rated light output - The sum of the initial rated lamp lumens of the lamp(s) that were supplied with the luminaire.
What are the disadvantages of adaptable ballasts?

Flexibility is the primary advantage of an adaptable ballast. However, before specifying, also consider the following disadvantages:

  • Increased cost
  • Unproven reliability
  • Increased ballast case size and weight
  • Variations in ballast factor for different lamp types
  • Lower efficacy

Cost. Initial cost is a concern for any lighting specifier. Adaptable ballasts for linear fluorescent lamps tend to carry a premium for their flexibility. However, adaptable ballasts for compact fluorescent lamps (CFLs) tend to have pricing similar to products that are dedicated to a single lamp/voltage combination. In the mature market for linear fluorescent ballasts, initial costs no longer include a premium to earn back the manufacturer’s development costs. The new designs for adaptable ballasts for linear fluorescent lamps thus cannot yet compete with commodity ballasts in terms of price. In the emerging CFL ballast market, however, most ballast designs are relatively new, and prices for adaptable ballasts are comparable to those for standard ballasts. According to John Andrews, Director of Operations for K-Tronic, as new CFLs came on the market CFL ballast manufacturers began engineering features such as adaptable voltage compatibility into their products from the start, so there is less of a pricing gap.

Reliability. Product reliability is a greater concern than cost for most users. Most adaptable ballasts are too new to have a proven record of meeting their rated life, and of providing rated life from the lamps they operate. To partially address this concern, most ballast manufacturers offer warranties of at least five years. However, if, in order to accommodate multiple lamp types, the ballasts are starting and operating the lamps at less than optimal conditions, there may be impacts on lamp life (Ji and Davis, 1994). NLPIP tests show that adaptable ballasts may operate lamps below their rated current, potentially reducing lamp life. However, adaptable ballasts typically have a separate circuit to heat lamp electrodes during lamp operation, mitigating the negative impact of low lamp current on lamp life.

Size/weight. Although some adaptable ballasts are available with “low profile” cases, the smallest adaptable ballasts are not quite as compact as the smallest non-adaptable ballast due to additional components. This is less of a concern for linear fluorescent lamps because most ballasts are roomy and sturdy enough to accommodate bulky ballasts. With compact fluorescent lamps, however, ballast weight and size are important considerations when designing luminaires.

Ballast factor. The measure of how close actual light output from a fluorescent lamp-ballast combination compared to the lamps’ rated light output is called the ballast factor (ANSI, 1984). Adaptable ballasts have ballast factors that can vary widely depending on lamp type. For a discussion of variations in ballast factor, see the section How Well Do Adaptable Ballasts Perform?

Efficacy. Adaptable ballasts may be less efficient than non-adaptable ballasts due to the power required for the additional circuitry that makes the ballast adaptable. This additional power requirement of the ballast results in a marginal increase to the combined lamp and ballast power, resulting in lower overall efficacy.

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