Xenon arc lamp
It produces a bright white light to simulate sunlight, with applications in movie projectors in theaters, in searchlights, and for specialized uses in industry and research.
[1] Interest in the xenon discharge was first aroused by P. Schulz in 1944, following his discovery of its near-continuous spectrum and high colour rendering white light.
[2] Owing to wartime limitations on the availability of this noble gas, significant progress was not made until John Aldington[3] of the British Siemens lamp company published his research in 1949.
[4] This triggered intensive efforts at the German Osram company to further develop the technology as a replacement for carbon arcs in cinema projection.
The xenon lamp promised tremendous advantages of a more stable arc with less flicker, and its non-consumable electrodes allowed longer films to be shown without interruptions.
Osram's primary contribution to this achievement was its thorough research of xenon discharge physics, which directed its developments towards very short arcs for DC operation with a particular electrode and bulb geometry.
The cathode is kept small to reach high temperatures for thermionic emission, the anode being larger to dissipate the heat generated as incoming electrons are decelerated.
Following these developments, the first successful public projection using xenon light was performed on 30 October 1950, when excerpts from a colour film (Schwarzwaldmädel) were shown during the 216th session of the German Cinematographic Society in Berlin.
As of 2016, laser illumination for digital theater projectors is starting to establish a market presence [8] and has been predicted to supersede the xenon arc lamp for this application.
Some lamps have envelopes made out of ultra-pure synthetic fused silica (such as "Suprasidh"), which roughly doubles the cost, but which allows them to emit useful light into the vacuum UV region.
To achieve maximum efficiency, the xenon gas inside short-arc lamps is maintained at an extremely high pressure — up to 30 atmospheres (440 psi / 3040 kPa) — which poses safety concerns.
In a pure xenon lamp, the majority of the light is generated within a tiny, pinpoint-sized cloud of plasma situated where the electron stream leaves the face of the cathode.
[citation needed] Because of these characteristics, xenon short-arc lamps require a proper power supply that operates without flickering in the flame, which could ultimately damage the electrodes.
Though not commonly known outside of Russia and the former Soviet satellite countries, long arc xenon lamps were used for general illumination of large areas such as rail stations, sports arenas, mining operations, and nuclear power plant high bay spaces.
This allowed the larger common sizes such as 5 and 10 kW to operate directly from mains AC at 110 and 220 volts respectively without a ballast – only a series igniter was necessary to start the arc.
They had the advantage of no mercury content, convective air cooling, no high pressure rupture risk, and nearly perfect color rendition.
Due to low efficiency and competition from more common lamp types, few installations remain today, but where they do, they can be recognized by a characteristic rectangular/elliptical reflector, and crisp blue-white light from a relatively long tubular source.
