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A light switch is a switch, commonly used to operate electric lights, permanently connected equipment, or electrical outlets. more...
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In modern homes most lights are operated using switches set in walls, usually 6-10 inches (15-25 cm) away from a door, to operate overhead ceiling lights. In torches (flashlight) the switch is often near the bulb, but may be in the tail, or even the entire head itself may constitute the switch (rotated to turn the light on and off).
Home light switches, being in reality a metal or plastic box with a switch in it, commonly have switch plate covers called wall plates. These are plastic, ceramic or metal, and 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.
A dimmer switch is a kind of light switch that allows a light to be dimmed or brightened continuously. Conceptually, a variable resistor in series with a lamp would allow adjustment of its brightness, but this would be inefficient and costly owing to power dissipated in the resistance as heat. Historically, and still used for some theatrical lighting, a variable autotransformer can be used to adjust the voltage applied to the lamps, and so, the brightness; but this equipment is too large to fit into a standard wall box. Solid-state thyristor switches allow for control of lighting by blocking part of the alternating current for an adjustable time delay, thereby allowing only part of the current through the dimmer and reducing the power input to the lamp. Nearly all dimmers use phase cutting systems based on triacs, controlled by a rotary or sliding knob or, more recently, a touch-sensitive plate. The components are small and low-cost and easily fit into wall boxes designed for on-off switches. Dimmers are intended only for use with permanently-installed lighting fixtures, and generally work best with incandescent lamps. Certain fluorescent fixtures used for commercial lighting can be dimmed, but these have special wiring requirements. Tungsten-halogen lamps may give unsatisfactory service life if operated on a dimmer since the internal redeposition of filament metal may not work properly at lower filament temperatures; see dimmer for more information.
History and culture
Light switches are usually built into the walls of the house. Surface mounting is also fairly common though is seen more in commercial industrial and outbuilding settings than in houses.
Because of electrical safety considerations in many countries their design and installation is regulated either by law or by widely accepted industry standards. In practice however in most countries any requirements for permits or certification are widely ignored and replacing a light switch is considered a simple "do-it-yourself" task with the parts being widely available.
Read more at Wikipedia.org
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