Neon lamp 303071 224568997 2008-07-09T13:33:48Z Mild Bill Hiccup 5202324 /* Description */ copyedit [[Image:Neon lamp.jpg|thumb|right||A small neon lamp (NE-2 type), with centimeter scale]] A '''neon lamp''' is a [[gas discharge]] [[Lamp|lamp]] containing primarily [[neon]] gas at low [[pressure]]. The term is sometimes used for similar devices filled with other [[noble gas]]es, usually to produce different colors. == Description == A small [[electric current]], which may be [[alternating current|AC]] or [[direct current|DC]], is allowed through the tube, causing it to glow orange-red. The exact formulation of the gas is typically the classic [[Penning mixture]], 99.5% [[neon]] and 0.5% [[argon]], which has lower [[Breakdown voltage|striking voltage]] than pure neon. The applied voltage must initially reach the striking voltage before the lamp can light. Once lit, the voltage required to sustain operation is significantly (~30%) lower. When driven from a DC source, only the negatively charged electrode ([[cathode]]) will glow. When driven from an AC source, both electrodes will glow (each during alternate half cycles). Neon lamps operate using a low current [[glow discharge]]. Higher power devices, such as [[mercury-vapor lamp]]s or [[metal halide lamp]]s use a higher current [[arc discharge]]. [[Image:Doutnavka.gif|thumb|Graph showing the relationship between current and voltage across a neon lamp.]] Once lit, a neon lamp has a [[negative resistance]] characteristic: increasing the current through the device increases the number of [[ion]]s, thereby decreasing the [[electrical resistance|resistance]] of the lamp and allowing even more current. (This behavior occurs between the points labeled A and B on the lamp's current vs. voltage graph.) Because of this characteristic, electrical circuitry external to the neon lamp must provide a means to limit current through the circuit or else the current will rapidly increase until the lamp is destroyed. For indicator-sized lamps, a [[resistor]] is conventionally used to limit the current. Larger [[neon sign]] sized lamps often use a specially constructed high voltage [[transformer]] to limit the available current, usually by introducing a large amount of [[leakage inductance]] in the secondary winding. When the current through the lamp is lower than the current for the highest-current discharge path, the [[glow discharge]] may become unstable and not cover the entire surface of the electrodes. This may be a sign of aging of the indicator bulb, and is exploited in the decorative "flicker flame" neon lamps. However, while too low a current causes flickering, too high a current increases the wear of the electrodes by stimulating [[sputtering]], which coats the internal surface of the lamp with metal and causes it to darken. [[image:neonowki.jpg|thumb|220px|Lit neon lamp, 220/230 volt and 110 V neon lamps and a screwdriver with neon lamp inside for use as a circuit tester.]] The flickering effect is caused by the differences of the ionization potential of the gas, which depends on spacing of the electrodes, temperature, ambient radiation, and the pressure of the gas. The potential needed to strike the discharge is higher than what is needed to sustain the discharge. When there is not enough current to ionize the entire volume of the gas around the electrodes, only partial ionization occurs and the glow forms around only part of the electrode surface. Convective currents make the glowing areas flow upwards, not unlike the discharge in a [[Spark gap#Spark gaps as entertainment|Jacob's ladder]]. A [[photoionization]] effect can also be observed here, as the electrode area covered with the discharge can be increased by shining light at the lamp. == Applications == [[Image:Nixie.gif|frame|left|The digits of a [[Nixie tube]].]] Most small neon (indicator-sized) lamps, such as the common '''NE-2''', break down at between 90 and 110 [[volt]]s. This feature enables their use as very simple [[voltage regulator]]s or [[overvoltage]] protection devices. In the 1960s [[General Electric]] ([[GE]]), Signalite, and other firms made special extra-stable neon lamps for electronic uses. They even devised digital [[logic circuit]]s, [[Binary numeral system|binary]] [[memory|memories]], and [[frequency]] dividers using neon lamps.<ref>J.W. Tuttle and C.R. Dougherty, ed.s, ''General Electric Glow Lamp Manual'' (East Cleveland, Ohio: General Electric Co., 1963). See especially the section "Logic and Computer Applications of Glow Lamps," which presents circuits using neon lamps in "and" gates, "or" gates, inverters, pulse generators, flip-flops, and ring counters. This section is available on-line at: http://computer-refuge.org/classiccmp/neon_lamp_logic/ . Click on "lamp.zip". The second (1966) edition of this booklet is available on-line here: http://www.tech-systems-labs.com/books/GE-lamps.pdf .</ref><ref>William G. Miller, ''Using and Understanding Miniature Neon Lamps'' (Indianapolis, Indiana: Howard W. Sams, 1969).</ref><ref>A.A. Vuylsteke, "Neon lamp flip-flop and binary counter," ''Electronics,'' vol. 26, page 248 (April 1953).</ref><ref>M.S. Raphael and A.S. Robinson, "Digital storage using neon tubes," ''Electronics'', vol. 29, pages 162-165 (July 1956).</ref><ref>Charles E. Hendrix, "A study of the neon bulb as a nonlinear circuit element," ''Proceedings of the Institute of Radio Engineers: Transactions on component parts'', vol. 3, no. 2, pages 44-54 (September 1956). (Use of neon lamps in "and" and "or" gates.)</ref><ref>J.C. Manley and E.F. Buckley, "Neon diode ring counter," ''Electronics'', vol. 23, pages 84-87 (January 1950).</ref><ref>R.L. Ives, "Neon oscillator rings," ''Electronics'', vol. 31, pages 108-115 (10 October 1958).</ref><ref>C.E. Hendrix and R.B. Purcell, "Neon lamp logic gates play tic-tac-toe," ''Electronics'', vol. 31, pages 68-69 (20 June 1958).</ref> Such circuits appeared in [[electronic organ]]s of the 1950s, as well as some instrumentation. At least some of these lamps had a glow concentrated into a small spot on the cathode, which made them unsuited to use as indicators. These were sometimes called "circuit-component" lamps, the other variety being indicators. A variant of the NE-2 type lamp, the NE-77, had three parallel wires (in a plane) instead of the usual two. It was also intended primarily to be a circuit component. Small neon lamps are used as indicators in electronic equipment. Called "tuneons" in 1930s radio sets, they were fitted as tuning indicators, and would give a brighter glow as the station was tuned in correctly. Larger lamps are used in [[neon signage]]. Neon lamps, due to their low current consumption, are used as [[nightlight]]s. Because of their comparatively fast response time, in the early development of [[television]] neon lamps were used as the light source in many [[Mechanical television|mechanical-scan TV]] displays. They were also used for a variety of other purposes; since a neon lamp can act as a [[relaxation oscillator]] with an added resistor and [[capacitor]], it can be used as a simple flashing lamp or [[sound|audio]] [[oscillator]]. (See [[Pearson-Anson effect]].) The use of neon lights in automobiles is becoming more common in today's growing custom car parts market. Neon lamps with several shaped electrodes were used as alphanumerical displays known as [[Nixie tube]]s. These have since been replaced by solid state devices. Novelty glow lamps with shaped electrodes (such as flowers and leaves), often coated with phosphors, have been made for artistic purposes. In some of these, the glow that surrounds an electrode is part of the design. [[Image:Glimmlampe spektrum.jpg|thumb|Unlit and lit neon lamps (NE-2 type) and their light [[spectrum]].]] In AC-excited lamps, both electrodes produce light, but in a DC-excited lamp, only the negative electrode glows. Thus a neon lamp can be used to distinguish between AC and DC sources and to ascertain the polarity of DC sources. Indicator-sized lamps can also be filled with [[argon]], [[krypton]], or [[xenon]] rather than neon, or mixed with it. While most operating characteristics remain similar, the lamps light with a bluish glow (including some [[ultraviolet]]) rather than neon's characteristic reddish-orange glow; the UV radiation then can be used to excite a [[phosphor]] coating of the inside of the bulb and provide a wide range of various colors, including white. A mixture of neon and [[krypton]] can be used for green glow. ==History== [[Nikola Tesla]] displayed his neon lights at the [[World's Columbian Exposition]] in 1893. His innovations in this type of light emission were not regularly patented. [[Georges Claude]] invented a neon lamp in 1902, and displayed it in public in 1910. == See also == *[[Timeline of lighting technology]] *[[1911 in science]] *[[List of light sources]] *[[Neon sign]] *[[Nixie tube]] ==Footnotes== {{reflist}} ==External links== {{Commonscat|Neon lamps}} * [http://ledmuseum.home.att.net/glow2.htm Neon lamps in LED Museum] {{ArtificialLightSources}} [[Category:Neon lighting]] [[Category:Vacuum tube displays]] [[Category:1902 introductions]] [[cs:Doutnavka]] [[el:Λαμπτήρας νέον]] [[es:Lámpara de neón]] [[fr:Lampe néon]] [[hr:Tinjalica]] [[it:Lampada al neon]] [[nl:Neonlamp]] [[ja:ネオン管]] [[pl:Lampa neonowa]] [[ru:Неоновая лампа]] [[sk:Tlejivka]] [[sv:Glimlampa]]