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What's the electronic metal halide ballast?
2013-05-24 07:28:50

Electronic ballasts are a relatively new offering, and they are now available for lamps of up to 600 W. They use switching electronics and small high-frequency inductors, rather than large line-frequency ones, to control current and voltage to the lamp. Though costly, electronic ballasts offer a host of benefits over their magnetic counterparts, including higher efficiency, better dimming capabilities, better light quality, and shorter warm-up times.

Electronic ballasts for HID lamps consume about 60 percent less power than their magnetic equivalents—a typical electronic ballast for a 400-W lamp uses 15 to 30 W, compared with 50 to 60 W for a magnetic ballast.

Light output. Metal halide lamps are notorious for the color variability of their light output, but lamps operated by electronic metal halide ballasts provide more stable output than lamps operated by magnetic ballast. That’s because the electronic ballasts reduce the variability of the voltage supplied to the lamp.

The light output of lamps driven by electronic ballasts also degrades more slowly over time, resulting in greater light output at the mean and end of the lamp’s life (see Figure 1). This in turn enables systems with electronic ballasts to use fewer fixtures, or lower-wattage lamps, to provide the same output as systems with magnetic ballasts.

An electronic metal halide ballast for igniting a discharge arc in a discharge tube of a metal halide lamp. The ballast includes ballast circuitry for periodically applying a voltage pulse having an amplitude of approximately 2-3 kilovolts to the discharge tube until ignition of the discharge arc is achieved. Each voltage pulse consists of a voltage pulse train having a frequency exceeding the acoustic resonance range of the discharge tube, preferably in a range of 2.5-3.0 megaHertz. A hot restart protection circuit of the ballast circuitry provides that the time period between voltage pulses is sufficient to permit cooling of the discharge tube during a time interval spanning application of a plurality of voltage pulses. Thus, even if the discharge tube is in a hot condition and, under such conditions, an amplitude of a voltage pulse necessary for ignition exceeds the 2-3 kilovolt amplitude of the ballast circuitry voltage pulses, the periodic application of voltage pulses to the discharge tube will permit cooling of the discharge tube and correspondingly lowering the amplitude of a voltage pulse necessary for ignition. When the required voltage pulse amplitude for ignition has been reduced to the electronic ballasts circuit voltage pulse magnitude ignition of an arc in the discharge tube will occur.

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