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Metal-halide lamp
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===Ballasts=== [[File:Osram POWERTRONIC PTi 35.JPG|thumb|upright=0.6|Electronic ballast for 35 W metal halide light bulbs]] The electric arc in metal-halide lamps, as in all [[gas discharge lamp]]s has a [[negative resistance]] property; meaning that as the current through the bulb increases, the [[voltage]] across it decreases. If the bulb is powered from a constant voltage source such as directly from the AC wiring, the current will increase until the bulb destroys itself; therefore, halide bulbs require [[electrical ballast]]s to limit the arc's current. There are two types: #''Inductive ballast'' - Many fixtures use an inductive ballast, also known as a magnetic ballast, similar to those used with [[fluorescent lamp]]s. This consists of an iron-core [[inductor]]. The inductor presents an impedance to AC current. If the current through the lamp increases, the inductor reduces the voltage to keep the current limited. #''Electronic ballast'' - These are lighter and more compact. They consist of an [[electronic oscillator]] which generates high frequency which is then converted to a low frequency square wave current to drive the lamp. Because they have lower resistive losses than an inductive ballast, they are more energy efficient. However, high-frequency operation does not increase lamp efficiency as for [[fluorescent lamp]]s. It may cause [[acoustic resonance]] in the arc, shortening the lamp life.<ref>{{Cite book |last1=Weibin |first1=Cheng |chapter-url=https://www.infona.pl//resource/bwmeta1.element.ieee-art-000001711902 |chapter=Suppressing Acoustic Resonance in HID Lamp with Combined Frequency Modulation |last2=Yanru |first2=Zhong |last3=Shun |first3=Jin |title=2006 37th IEEE Power Electronics Specialists Conference |date=2006 |pages=1β5 |doi=10.1109/PESC.2006.1711902 |isbn=978-0-7803-9716-3 |language=English}}</ref> Pulse-start metal-halide bulbs don't contain a starting electrode which strikes the arc, and require an ignitor to generate a high-voltage (1β5 kV on cold strike, over 30 kV<ref name=ecm>{{cite web|url=https://www.ecmweb.com/content/minimize-hid-lighting-system-downtime |title=Minimize HID Lighting System Downtime |website=Electrical Construction & Maintenance |access-date=20 September 2018 |quote=Instant restrike and quick restart systems eliminate the delay in restarting MH lamps after a sag or interruption. They use specially wired CWA ballasts and high-voltage ignitors that produce a high voltage (8kV to 40kV) to restart special lamps.|date=September 1998 }}</ref> on hot restrike) pulse to start the arc. Electronic ballasts include the igniter circuit in one package. [[American National Standards Institute]] (ANSI) lamp-ballast system standards establish parameters for all metal-halide components (with the exception of some newer products).
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