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Flashlight | المصباح الكهربائي
A Flashlight (usually called a torch outside North America) is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode (LED). Typical flashlight designs consist of the light source mounted in a parabolic or other shaped reflector, a transparent lens to protect the light source from damage and debris, a power source (typically electric batteries), and an electric power switch.
While most flashlights are hand-held, there are head or helmet-mounted flashlights designed for miners and campers and battery-powered lights for bicycles. Some flashlights are powered by hand-cranked dynamos or electromagnetic induction or are recharged by solar power.
The name flashlight is used mainly in the United States and Canada. In other English-speaking countries, the more common term is torch or electric torch.
In 1896, the first dry cell battery was invented. Unlike previous batteries, it used a paste electrolyte instead of a liquid. This was the first battery suitable for portable electrical devices, as it did not spill or break easily and worked in any orientation.
On January 10 1899, American Electrical Novelty and Manufacturing Company obtained U.S. Patent No. 617,592 (filed 12 March 1898) from David Misell, its English inventor This "electric device" designed by Misell was powered by "D" batteries laid front to back in a paper tube with the light bulb and a rough brass reflector at the end. The company donated some of these devices to the New York City police, who responded favorably to them.
These early flashlights ran on zinc–carbon batteries, which could not provide a steady electric current and required periodic 'rest' to continue functioning. Because these early flashlights also used energy-inefficient carbon-filament bulbs, "resting" occurred at short intervals. Consequently, they could be used only in brief flashes, hence the popular name flashlight.
Incandescent flashlights use incandescent lamps which consists of a glass bulb and a tungsten filament. Tungsten filament gives off radiant energy in spectrum corresponding to its temperature. The bulbs are under vacuum or filled with argon, krypton or xenon and sometimes a trace of halogen such as iodine or bromine. An example of incandescent flashlight is the Maglite by Mag Instrument, which can produce 2.3 (Maglite Solitare)to 218 lumens(MagCharger)
Recently, flashlights that use light-emitting diodes (LEDs) instead of conventional lightbulbs have become available. LEDs have existed for decades, mainly used as low-power indicator lights. In 1999, Lumileds Corporation of San Jose, California United States, introduced the Luxeon LED, a high-power white-light emitter. For the first time this made possible LED flashlights with power and running time better than some incandescent lights. The first Luxeon LED flashlight was the Arc LS, designed in 2001.
LEDs can be significantly more efficient than incandescent lamps at lower power levels, so they use less battery energy than incandescent lightbulbs. Such flashlights have longer battery lifetimes, in some cases, hundreds of hours, although the LED efficiency advantage diminishes at higher power levels. LEDs are also less fragile than conventional glass lamps.
Some LED flashlights electronically regulate the voltage supplied to the LEDs to reduce the influence of battery status on light output. By contrast, the light output of non-regulated flashlights change proportionally to the voltage supplied by the battery resulting in a significant decline in output as battery voltage declines. LEDs also have the advantage of maintaining a specific color temperature regardless of input voltage or current, while the color temperature of an incandescent bulb declines with the power available
While lower-power LED flashlights generate very little heat, more powerful LED lights do generate significant amounts of heat mostly as the semiconductor junction inherently dissipates heat. For this reason higher-powered LED flashlights usually[clarification needed] have aluminum bodies and can become quite warm during use. The aluminum bodies act as a heatsink for the LED(s).
Another less common type of flashlight uses a High Intensity Discharge (HID) lamp as the light source. HID is a type of gas discharge lamp that uses a mixture of metal halide salts and argon as a filler.
Some advantages of this design are that they produce more light than an incandescent flashlight using the same amount of electricity, the lamp will last longer and they are more shock resistant than a regular incandescent bulb, as they lack the relatively fragile electrical filament found in incandescent bulbs. However; they are much more expensive (due to the need for a ballast and other circuitry to start and operate the lamp). An example of an HID flashlight is the Surefire Hellfire Weaponlight.
A headlamp is a flashlight designed to be worn on the head. A headlamp usually consists of the light emitter at the front, with a battery pack also attached to the front or back. The battery pack may be attached to the back to improve balance.
Sometimes a tactical light is mounted to a handgun or rifle. See also Streamlight and SureFire.
Most flashlights are cylindrical in design, with the lamp assembly attached to one end. However, early designs came in a variety of shapes. Many resembled modern day lanterns, consisting largely of a box with a handle and the lamp attached to the front. Some others were made to have a similar appearance to candles.
Although most flashlights are designed in a manner that allows the user to replace the batteries and the bulb as needed, fully-sealed disposable flashlights do exist, such as the Garrity Life Lite, and various inexpensive keyring lights. When the batteries in a disposable flashlight are depleted or the bulb fails, the entire product usually is thrown away or recycled and a new one purchased to replace it.
The most common power source for flashlights is the battery. Many types of batteries are suitable for use in flashlights, such as button cells, alkaline batteries, lithium batteries and rechargeable NiMH, NiCd batteries and lithium ion batteries. The choice of batteries will depend on the light source used, and will usually play a determining role in the form factor of the flashlight.
Some flashlights are solar powered, using the energy generated from a solar cell to charge an on-board battery for later use.
Some flashlights have an electrical generator built into them. One type of dynamo-powered flashlight has a winding crank connected to a small alternator that feeds several diode bridges with their outputs connected in parallel feeding a field effect transistor that charges a capacitor that connects to one or more LEDs. Others generate electricity using electromagnetic induction. They use a strong permanent magnet that can freely slide up and down a tube, passing through a coil of wire as it does. Shaking the flashlight will charge a capacitor or a rechargeable battery that supplies a current to a light source, typically a light-emitting diode or, more rarely, an incandescent light bulb. Such flashlights can be useful during an emergency, when batteries may not be available.
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