Arc lamp, also known as arc light is used for a group of lamps that create light with the help of an electric arc. The lamp is made of two electrodes that were earlier made of carbon but today these are made from tungsten. The electrodes are separated by a gas and the kind of lamp is often named after the kind of gas used. For example, xenon arc lamp uses xenon gas. Other gases that are used include krypton, neon, argon, mercury, metal halide, sodium etc. Carbon arc lamps use electrode made of carbon. The common arc lamps that you see in the market are a low-pressure mercury arc lamp.
How arc lamps work
The electric arc, consisting of gas, is initially ionized by passing a high voltage, which then becomes electrically conductive. To start the arc lamp, a very high voltage is passed with the help of an electrical circuit with the ballast and an ignite. The ballast is wired in a sequence with the lamp. The result is th development of a high voltage across the ballast for a moment and as the lamp is connected to the ballast, it gets this high voltage that lights up the arc within the tube/lamp. The cycle is repeated till the lamp is ionized enough to maintain the arc.
In general terms, when we refer to arc lamp, we mean carbon arc lamp only. The electrodes in these lamps are made of carbon and to ignite the lamp, the rods are brought in contact with each other. This leads to a low striking the arc. The rods, when separated slowly, cause the electric current to heat and maintain an arc across the gap.
Today you will come across various uses of carbon arc lamp as well as xenon arc lamp in different fields for various purposes. These lamps are known to produce light 10 to 100 times brighter than the incandescent light. The mercury arc lamps can produce light at a certain spectrum, which allows the scientists to study the microscopic world. Arc lamps were used in earlier times in motion-picture studios to light up the interior shots.
Arc lamps were soon outmoded by more competent and longer-lasting filament lamps.