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Gas-filled tube
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<p>A gas-filled tube, also commonly known as a discharge tube or formerly as a <a href="/facts/Julius_Pl%C3%BCcker/QgoMT64G">Plücker</a> tube, is an arrangement of <a href="/facts/Electrode/251PaKX8">electrodes</a> in a <a href="/facts/Gas/hVVAoodV">gas</a> within an <a href="/facts/Dielectric/PnVt9P2G">insulating</a>, temperature-resistant <a href="/facts/Envelope/25KewVgd">envelope</a>. Gas-filled tubes exploit phenomena related to <a href="/facts/Electric_discharge_in_gases/IBvwoujy">electric discharge in gases</a>, and operate by <a href="/facts/Ionisation/W13Ceavd">ionizing</a> the gas with an applied <a href="/facts/Voltage/EN2po6N2">voltage</a> sufficient to cause <a href="/facts/Electrical_conduction/akyCKvMy">electrical conduction</a> by the underlying phenomena of the <a href="/facts/Townsend_discharge/W69jPeBw">Townsend discharge</a>. A <a href="/facts/Gas-discharge_lamp/SQPgULuM">gas-discharge lamp</a> is an <a href="/facts/Electric_light/v3fb5WBp">electric light</a> using a gas-filled tube; these include <a href="/facts/Fluorescent_lamp/R8SlXCyg">fluorescent lamps</a>, <a href="/facts/Metal-halide_lamp/kxCKb1E9">metal-halide lamps</a>, <a href="/facts/Sodium-vapor_lamp/STEH8FgR">sodium-vapor lamps</a>, and <a href="/facts/Neon_light/RIo03t4t">neon lights</a>. Specialized gas-filled tubes such as <a href="/facts/Krytron/VjcEDoM2">krytrons</a>, <a href="/facts/Thyratron/tkhB15CK">thyratrons</a>, and <a href="/facts/Ignitron/M0tGxglG">ignitrons</a> are used as switching devices in electric devices. </p><p>The voltage required to initiate and sustain discharge is dependent on the <a href="/facts/Pressure/eyc37GRG">pressure</a> and composition of the fill gas and geometry of the tube. Although the envelope is typically glass, power tubes often use <a href="/facts/Ceramic/9JKudpqX">ceramics</a>, and military tubes often use glass-lined metal. Both <a href="/facts/Hot_cathode/UPYcHmhg">hot cathode</a> and <a href="/facts/Cold_cathode/da9mlNne">cold cathode</a> type devices are encountered. </p>