Editing Neon lamp (section)

== Description ==
[[File:Glow discharge current-voltage curve English.svg|thumb|right|300px|Voltage-current characteristics of electrical discharge in neon at 1 torr, with two planar electrodes separated by 50&nbsp;cm.<br/>
A: random pulses by [[cosmic radiation]]<br/>
B: saturation current<br/>
C: [[Avalanche breakdown]] Townsend discharge<br/>
D: self-sustained [[Townsend discharge]]<br/>
E: unstable region: [[corona discharge]]<br/>
F: sub-normal glow discharge<br/>
G: normal glow discharge<br/>
H: abnormal glow discharge<br/>
I: unstable region: glow-arc transition<br/>
J: [[electric arc]]<br/>
K: electric arc<br/>
'''A-D region: dark discharge'''; ionisation occurs, current below 10 microamps.<br/>
'''F-H region: glow discharge'''; the plasma emits a faint glow. <br/>
'''I-K region: arc discharge'''; large amounts of electromagnetic radiation produced.]]
A small [[electric current]] (for a 5&nbsp;mm bulb diameter NE-2 lamp, the [[quiescent current]] is about 400 μA), which may be [[alternating current|AC]] or [[direct current|DC]], is allowed through the tube, causing it to glow orange-red. The gas is typically a [[Penning mixture]], 99.5% [[neon]] and 0.5% [[argon]], which has lower [[Breakdown voltage#Gases and vacuum|striking voltage]] than pure neon, at a pressure of {{Convert|1-20|torr||abbr=}}.

The lamp [[glow discharge]] lights at its striking voltage.<ref name="MILLER69">{{cite book |title=Using and Understanding Miniature Neon Lamps |url=https://archive.org/details/UsingAndUnderstandingMiniatureNeonLamps |last=Miller |first=William G. |publisher=Howard W Sams & Co, Inc. |location=Indianapolis |date=1969}}</ref> The striking voltage is reduced by ambient light or radioactivity. To reduce the "dark effect", some lamps were made with a small amount of radioactive material, typically [[Krypton-85]], added to the envelope to provide ionization in darkness.<ref name=MILLER69/> 

The voltage required to sustain the discharge is significantly (up to 30%) lower than the [[Breakdown voltage|striking voltage]]. This is due to the organization of positive ions near the cathode.  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]]. Low pressure [[sodium-vapor lamp]]s use a neon Penning mixture for warm up and can be operated as giant neon lamps if operated in a low power mode. 

===Limiting current===
Once the neon lamp has reached breakdown, it can support a large current flow. Because of this characteristic, electrical circuitry external to the neon lamp must limit the current through the circuit or else the current will rapidly increase until the lamp is destroyed. 

For indicator-sized lamps, a [[resistor]] typically limits the current. In contrast, larger sized lamps often use a specially constructed high voltage [[transformer]] with high [[leakage inductance]] or other [[electrical ballast]] to limit the available current (see [[neon sign]]).

===Flicker flame===
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 [[Electrode|electrodes]].<ref name="Glow Lamp Manual">{{cite book |first1=C. R. |last1=Dougherty |first2=T. D. |last2=Foulke |first3=J. D. |last3=Harden |first4=T. L. |last4=Hewitt |first5=F. N. |last5=Peters |first6=R. D. |last6=Smith |first7=J. W. |last7=Tuttle |title=General Electric Glow Lamp Manual |edition=2nd |publisher=General Electric Company |date=1966}}</ref> This may be a sign of aging of the indicator lamp, 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.

The potential needed to strike the discharge is higher than what is needed to sustain the discharge. When there is not enough current, 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 by the glow discharge can be increased by shining light at the lamp.

===Efficiency===
In comparison with [[incandescent lamps]], neon lamps have much higher [[luminous efficacy]]. [[Incandescence]] is heat-driven light emission, so a large portion of the electric energy put into an incandescent lamp is converted into heat. Non-incandescent light sources such as neon lamps, [[fluorescent lamp]]s, and [[light-emitting diodes]] are therefore much more energy efficient than normal incandescent lamps. LEDs are the highest efficiency. 

[[Green]] neon lamps<ref>{{Cite web |title=Neon Lamps, Neon Indicator Lamps {{!}} ILT |url=https://internationallight.com/applications/neon-lamps |access-date=2025-05-16 |website=internationallight.com}}</ref> can produce up to 65 lumens per watt of power input, while white neon lamps have an efficacy of around 50 lumens per watt. In contrast, a standard incandescent lamp only produces around 13.5 lumens per watt.<ref>{{cite web|first=Marcus|last=Thielen|title=LED or Neon|url=http://www.signweb.com/index.php/channel/12/id/138/|date=2006-02-10|access-date=2008-12-30|url-status=dead|archive-url=https://web.archive.org/web/20080409004409/http://www.signweb.com/index.php/channel/12/id/138|archive-date=2008-04-09}}</ref>

===Environmental effects===
The precise values of starting and maintaining voltages of neon lamps is subject to change due to several effects. External light falling on the electrodes provides a source of ionization to start the lamp; in total darkness, lamps may reach a high and erratic starting voltage. One measure to mitigate for this effect is to include a pilot lamp within the enclosure to provide an initial source of light. Lamps are also somewhat sensitive to external electrostatic fields, temperature, and aging. Lamps intended for use as circuit components may be specially processed to eliminate most of the initial aging effects.<ref name=GE/>