ARC LAMP

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Arc Lamp was invented by - C.F.Brush.




"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc (also called a voltaic arc). The lamp consists of two electrodes, first made from carbon but typically made today of tungsten, which are separated by a gas. The type of lamp is often named by the gas contained in the bulb; including neon, argon, xenon, krypton, sodium, metal halide, and mercury, or by the type of electrode as in carbon-arc lamps. The common fluorescent lamp is a low-pressure mercury arc lamp.

An arc is the discharge that occurs when a gas is ionized. 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 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 rated 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.

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).

Carbon arc lamp

In popular use, the term arc lamp means carbon arc lamp only. In a carbon arc lamp, the electrodes are carbon rods in free air. To ignite the lamp, the rods are touched together, thus allowing a relatively low voltage to strike the arc. The rods are then slowly drawn apart, and electric current heats and maintains an arc across the gap. The tips of the carbon rods are heated to incandescence, creating light. The rods are slowly burnt away in use, and the distance between them needs to be regularly adjusted in order to maintain the arc. Many ingenious mechanisms were invented to effect this automatically, mostly based on solenoids. In the simplest form (which was soon superseded by more smoothly acting devices) the electrodes are mounted vertically. The current supplying the arc is passed in series through a solenoid attached to the top electrode. If the points of the electrodes are touching (as in start up) the resistance falls, the current increases and the increased pull from the solenoid draws the points apart. If the arc starts to fail the current drops and the points close up again.

Water-wall plasma arc lamp

The Vortek water-wall plasma arc lamp, invented in Vancouver, Canada, made the Guinness Book of World Records in 1986 and 1993 as the most powerful continuously burning light source at over 300 kW or 1.2 million candle power. The Vortek lamp was produced by Vortek Industries until October 2004 when Mattson Technology purchased Vortek Industries. Mattson claims continuous power of up to 750 kW and flash lamp energy of 100kJ.

The Vortek lamp was invented by David Camm and Roy Nodwell at the University of British Columbia in 1975. The key innovation is to protect the quartz glass tube from the 12000 °C heat of the arc with a layer of water flowing in a spiral on the inside surface of the tube.

Vortek lamps are used commercially in the Mattson Millios millisecond anneal system for processing semiconductor wafers. Other uses include solar simulation and processing of coating materials.

Starting in 1999, the U.S. Oak Ridge National Laboratory (ORNL) Infrared Processing Center operated a 300 kW Vortek lamp to deliver 3500 watts/cm2 in an infrared beam capable of irradiating areas 10 to 35 cm wide. In 2003 a new 750 kW plasma arc lamp was installed at ORNL IPC with uniform irradiance of 460 W/cm2 over an area of 375 cm2.

In 2011, MesoCoat, a subsidiary of Abakan Inc., announced a multi-year agreement with Mattson to use Vortek lamps for developing nano-composite metal cladding processes for steel pipes or other metal parts used in harsh environments.