An arc lamp, or arc light, is a type of lamp that creates light via an electric arc. The two electrodes that are inside of an arc lamp are separated by gas. Thus, any lamp containing gas is usually called by the name of the gas that is inside of it. Neon, xenon, mercury, and krypton lamps are all considered arc lights.
The gas inside of an arc lamp is ionized due to an extremely powerful voltage. When an arc light is turned on, an immense amount of volts are sent through the lamp. This ignite the gas inside of the lamp. Thus, in order to use an arc lamp, an electrical circuit must contain a ballast, which controls the amount of current inside an electrical outlet, and an igniter.
When replacing an arc lamp, all parts -- including the ballast, igniter, and the actual lamp -- must match. If arc light parts do not match, then the lamp will not work. In addition to the types of arc lamps listed above, the common fluorescent lamp is also considered an arc lamp of low voltage.
Sir Humphry Davy created the first arc light around 1807. Humphry used two charcoal sticks in conjunction with a 2000-cell battery in order to make an arc light. Davy named the light an "arch lamp" due to the curved light that was emitted from the lamp. During the 1880s, arc lights were placed throughout public areas, since these lights proved to be much more powerful than the popular filament lamps that were frequently used.
During the 1900s, arc lamps were used on indoor movie sets in order to create a large amount of light. The main problem with this use of the arc lamp was that the light was far too bright -- actors had to wear sunglasses when not shooting to avoid eye strain. Eventually, set designers figured out that adding a plain window pane to the front of the light could effectively filter out the harsh light.
When the "talkies" rolled around, the arc light was no longer used on movie sets. Today, some carbon arc lights still exist, though most of these lights are being replaced by xenon arc lamps. Homeowners will find that shopping for a traditional arc lamp is somewhat difficult, though some of these lamps can still be found within antique shops. An arc light that is used inside of a home will create an interesting lighting effect.