Editing Arc lamp (section)

== Operation ==
<!-- This section focuses too much on the gas tube with HV DC ignition; touching also works; see carbon arc section -->
An ''arc'' is the discharge that occurs when a gas is [[ion]]ized. A high voltage is pulsed across the lamp to "ignite" or "strike" the arc, after which the discharge can be maintained at a lower voltage. The "strike" requires an electrical circuit with an ''igniter'' and a [[Electrical ballast|ballast]]. The ballast is wired in series with the lamp and performs two functions.

First, when the power is first switched on, the igniter/starter (which is wired in parallel across the lamp) sets up a small current through the ballast and starter. This creates a small magnetic field within the ballast windings. A moment later the starter interrupts the current flow from the ballast, which has a high inductance and therefore tries to maintain the current flow (the ballast opposes any change in current through it); it cannot, as there is no longer a 'circuit'. As a result, a high voltage appears across the ballast momentarily, to which the lamp is connected; therefore the lamp receives this high voltage across it which 'strikes' the arc within the tube/lamp. The circuit will repeat this action until the lamp is ionized enough to sustain the arc.

When the lamp sustains the arc, the ballast performs its second function, to limit the current to that needed to operate the lamp. The lamp, ballast, and igniter are rating-matched to each other; these parts must be replaced with the same rating as the failed component or the lamp will not work.

The colour of the light emitted by the lamp changes as its electrical characteristics change with temperature and time. [[Lightning]] is a similar principle where the atmosphere is ionized by the high potential difference (voltage) between earth and storm clouds.

[[Image:Ion spectral line radiation from a krypton arc lamp.JPG|thumb|200px|A krypton arc lamp during operation.]]
The temperature of the arc in an arc lamp can reach several thousand degrees Celsius. The outer glass envelope can reach 500 degrees Celsius, therefore before servicing one must ensure the bulb has cooled sufficiently to handle. Often, if these types of lamps are turned off or lose their power supply, one cannot restrike the lamp again for several minutes (called cold restrike lamps). However, some lamps (mainly fluorescent tubes/energy saving lamps) can be restruck as soon as they are turned off (called hot restrike lamps).

The Vortek water-wall plasma arc lamp, invented in 1975 by David Camm and Roy Nodwell at the [[University of British Columbia]], Vancouver, Canada, made the Guinness Book of World Records in 1986 and 1993 as the most powerful continuously burning light source at over 300&nbsp;kW or 1.2 million candle power.<ref>{{cite book|last=Voyer|first=Roger|title=The New Innovators: How Canadians Are Shaping the Knowledge-Based Economy|year=1994|publisher=James Lorimer & Company Ltd.|location=Toronto|isbn=978-1-55028-463-8|pages=[https://archive.org/details/newinnovatorshow0000voye/page/20 20]|url-access=registration|url=https://archive.org/details/newinnovatorshow0000voye/page/20}}</ref>