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.
Why should I use adaptable ballasts?

The primary reason to use an adaptable ballast is the convenience that its flexibility offers. Users that can benefit from this flexibility include:

Facility managers. Those who are responsible for a large facility with many different types of ballasts can reduce their replacement ballast inventories by stocking adaptable ballasts compatible with their various lighting systems. When servicing luminaires, the chance of installing the wrong ballast type is reduced. Also, when a facility manager is called to service a luminaire it won’t be necessary to first make a trip to check inside the fixture and get the specs before going to the stockroom to find the right ballast. Also, if the adaptable ballasts support different lamp quantities and the luminaires have the proper sockets and optical design to allow it, light levels (and energy use) can easily be adjusted to suit a space’s current use by adding or subtracting lamps from luminaires (see Figure 2). Light levels may also be increased or decreased by using higher or lower wattage lamps. Beyond task tuning, these methods can also be used for load shedding.

Figure 2. Flexibility advantage of adaptable ballasts
Office application Drafting application

Application flexibility is a primary advantage of adaptable ballasts. In the example above, an office has four 2x2 luminaires that can each accommodate four T5 twin-tube lamps. With adaptable ballasts, if the room is reconfigured from an office space into a drafting area, lamps can be added or removed from the luminaires to achieve the desired light distribution without any need for changing the ballasts. If the drafting tables require higher light levels than the desks in the office application, higher-wattage T5 twin-tube lamps can be used to increase the luminaires’ light output.

Electrical contractors and installers. Because they typically work on many diverse projects, contractors spend a great deal of effort matching ballasts with luminaires. If the lighting specifications for a project change partway through a project, contractors may be left with too many of one type of ballast and not enough of another. They may face work delays if their distributor backorders a specific ballast. Adaptable ballasts allow contractors to simplify the ballast selection process. Contractors also may potentially save money via quantity discounts by purchasing adaptable ballasts for several projects at once.

Luminaire manufacturers. Most fluorescent luminaires are sold with ballasts installed. The luminaire manufacturer must carefully manage the ballast inventory to make sure they have sufficient supply to keep their assembly lines productive. Adaptable ballasts allow manufacturers to reduce their total ballast inventory, and reduce the chances that they will run out of a particular ballast or install the wrong ballast. Luminaires equipped with adaptable ballasts can potentially be marketed at a premium, based on multiple voltage capacity and the ability to operate without a full complement of lamps installed. However, due to added circuitry, adaptable ballasts may not be as small as simpler ballasts and may be more difficult to fit into existing luminaires. This is especially true for compact fluorescent lamp (CFL) ballasts, which are typically much smaller than those for linear fluorescent lamps.

Lighting specifiers. Architects and lighting designers can also benefit by specifying adaptable ballasts. Then, last minute changes to the client's preferred luminaire type or to the electrical wiring plans won't necessarily mean that the ballast must be re-specified. Implementation and commissioning of the lighting design may also run smoother if the electrical contractors find their jobs simplified by adaptable ballasts.

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