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Flashlight
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A flashlight (also called a torch) is a portable electric spotlight which emits light from a small incandescent lightbulb, or from one or more light-emitting diodes (LEDs). The light source is mounted in a housing which contains a parabolic reflector, a clear protective lens, a power source (typically electric batteries), and an electric power switch.
While most flashlights are intended to be held in the hand, there are also helmet-mounted flashlights designed for miners and campers.
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Encyclopedia
A flashlight (also called a torch) is a portable electric spotlight which emits light from a small incandescent lightbulb, or from one or more light-emitting diodes (LEDs). The light source is mounted in a housing which contains a parabolic reflector, a clear protective lens, a power source (typically electric batteries), and an electric power switch.
While most flashlights are intended to be held in the hand, there are also helmet-mounted flashlights designed for miners and campers. Some types of flashlights can be powered by hand-cranked dynamos, electromagnetic induction or 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.
History
In 1898, Joshua Lionel Cowen invented a decorative lighting fixture for potted plants which consisted of a metal tube housing a light bulb and a dry cell battery. It failed commercially, and so Cowen sold his company and patents to Conrad Hubert that same year and turned his attention to building and selling model trains. Hubert renamed Cowen's company the American Electrical Novelty & Manufacturing Company and, recognizing the true potential of Cowen's invention, hired David Misell to produce a tubular flashlight for portable use.
They donated some models to the New York City police, who responded favorably to it. These early flashlights ran on zinc-carbon batteries, which were poor at providing sustained currents; they would run down after a while and needed to rest before being usable again. Since these early flashlights also used energy-inefficient carbon filament bulbs, this happened rather quickly, and consequently they could only be used in brief flashes, hence the popular name flashlight.
General information
A typical flashlight consists of a small incandescent lightbulb (or, in recent models, an LED) with associated parabolic reflector, powered by electric batteries, and with an electric power switch. The components are mounted in a housing that contains the necessary electric circuit and provides ease of handling, a means of access to the batteries for replacement, and a clear covering over the lightbulb for its protection.
Although a relatively simple device, its invention did not occur until the late 19th century because it depended upon the earlier invention of the electric battery and incandescent light bulb.
Incandescent
Incandescent flashlights use bulbs that contain a heated-up coil of tungsten wire, which gives off light energy as well as heat. The bulbs are filled with gas (usually argon, perhaps with a trace of a halogen: in higher quality models, xenon is used). A popular example of an incandescent flashlight is the Maglite by Mag Instrument and are capable of producing 40 to 50 lumens .
LED
Recently, flashlights which use light-emitting diodes (LEDs) instead of conventional lightbulbs have become available.
LEDs have existed for decades, mainly 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 in 2001.
LEDs can be significantly more efficient at lower power levels and so use less battery energy than ordinary lightbulbs. Such flashlights have longer battery lifetimes, in some cases hundreds of hours, although the LED efficiency advantage diminishes at higher power levels. LEDs also survive sharp blows that often break conventional lightbulbs.
LED flashlights are often electronically regulated to maintain constant light output as the batteries fade. By contrast a non-regulated flashlight becomes progressively dimmer, sometimes spending much of the total running time below 50 percent brightness level.
While lower-power LED flashlights generate little heat, more powerful LED lights do generate significant amounts of heat – although not as radiant energy, as the semiconductor junction inherently dissipates heat. For this reason higher-powered LED flashlights usually have aluminum bodies and can become quite warm during use. The use of aluminum is largely due to its thermal properties, acting as a heatsink for the high-power LED. Very few high-output LED flashlights use a plastic body due to plastic's being a thermal insulator rather than a conductor.
HID
Another less common type of flashlight uses a High Intensity Discharge (HID) lamp as the light source. HID lamps work by discharging an electric current between 2 electrodes in a capsule filled with a mixture of metal halide salts and argon, producing an extremely bright light.
Some advantages of this design are that they produce more light than an incandescent flashlight using the same amount of electricity, and the lamp will last longer and is more shock resistant than a regular incandescent bulb. However, they are much more expensive (due to the need for a ballast and other circuitry to start and operate the lamp) and are usually rather bulky. An example of an HID flashlight is the Surefire Hellfire Weaponlight.
Other designs
A headlamp is a flashlight worn on the head for hands-free operation. Powerful headlamps mounted on helmets have been used in mining for decades, but general-purpose ones with fabric straps are now also available.
Sometimes a 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 lanterns of the day, 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.
High-end flashlights
High end lights often go for as much as several hundreds of pounds/euros/dollars. Using metals such as titanium, steel, or even silver, and often being limited in production they often end up as collector's items trading at many times their original sales price. Such flashlights are very advanced, using special batteries, have adjustable brightness levels, waterproof ratings, and are very bright.
Power sources
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 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.
Mechanical power
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.
See also
External links
— Flashlight Museum
— The New Flashlight Reviews site with excellent pictures, flashlight care and batteries info
— Legendary Flashlight Reviews, Lots of good & valuable information
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