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.
How do adaptable ballasts work?

Adaptable ballasts that accommodate multiple lamp type and lamp quantity combinations generally can only do so if the lamp combinations yield roughly the same total lamp current. Thus, it would be unusual to find a ballast that can operate either one 15-watt lamp or two 40-watt lamps, for example. The total lamp current of these two combinations are too different for even an adaptable ballast to handle. Manufacturers could incorporate advanced load sensing circuitry to overcome this limitation, but it would make the ballasts prohibitively expensive.

Instead, manufacturers typically offer a small range of adaptable ballasts to cover most possible lamp combinations. For example, Advance Transformer's SmartMate™ product line includes four models, each of which operates five to ten different lamp combinations, providing coverage for about 25 different combinations between them.

To accommodate different input voltages, some adaptable ballasts have special digital circuitry that detects input voltage and adjusts power characteristics accordingly. These universal input ballasts typically can handle input voltages over a wide continuous range, such as 90V to 308V, and may also work with either 60Hz or 50Hz power systems.

At least one manufacturer (Fulham, Inc.) uses a different approach to achieve flexibility. Rather than having a single circuit that adapts itself to different voltages and loads, and a single set of wires to connect to power and the lamps, the Fulham ballast uses multiple built-in circuits, each with its own set of wires.


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