There are three light switches on a wall one of the switches controls a light?

In building wiring, a light switch is a switch, most commonly used to operate electric lights, permanently connected equipment, or electrical outlets. Portable lamps such as table lamps will have a light switch mounted on the socket, base, or in-line with the cord. Manually operated on/off switches may be substituted by remote control switches, or light dimmers that allow controlling the brightness of lamps as well as turning them on or off.

Light switches are also found in flashlights and automobiles and other vehicles. Switches for lighting may be in hand-held devices, moving vehicles and buildings. Residential and commercial buildings usually have wall-mounted light switches to control lighting within a room.

Mounting height, visibility, and other design factors vary from country to country. Switches are often recessed within a finished wall. Surface mounting is also fairly common though is seen more in commercial industrial and outbuilding settings than in houses.

A light switch box (a pattress box) has a plastic, ceramic or metal cover to prevent accidental contact with live terminals of the switch. Wall plates are available in different styles and colours to blend in with the style of a room. The first light switch employing quick-break technology was invented by John Henry Holmes in 1884 in the Shieldfield district of Newcastle upon Tyne.

1 The "quick-break" switch overcame the problem of a switch's contacts developing electric arcing whenever the circuit was opened or closed. Arcing would cause pitting on one contact and the build-up of residue on the other, and the switch's useful life would be diminished.