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Variable-output, digitally regulated flashlight


A flashlight (called a torch outside North America) is a portable electric spotlight that emits light from a small incandescent lightbulb or from one or more light-emitting diode (LEDs). Typical flashlight designs usually consist of the light source in a parabolic reflector or specially shaped lens to shape the flashlight beam, a transparent window to protect the light source from damage and debris, a power source (typically electric batteries), and an electric power switch.

While most flashlights are intended to be hand-held, there are also 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 Statesmarker and Canadamarker. In other English-speaking countries, the more common term is torch or electric torch.

History

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 10 January 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 were incapable of providing a steady source of electric current and needed to be 'rested' periodically to continue functioning. Because these early flashlights also used energy-inefficient carbon-filament bulbs, this occurred at short intervals. Consequently, they could be used only in brief flashes, hence the popular name flashlight.

Incandescent

Incandescent flashlights use incandescent bulbs containing a electrical filament of tungsten wire, which gives off light energy as well as heat. The bulbs are evacuated with an inert gas (usually argon, sometimes with traces of halogen: in higher quality models, xenon is used). A popular example of an incandescent flashlight is the Maglite by Mag Instrument which are capable of producing 40 to 50 lumens [33350].

LED

Recently, flashlights which use light-emitting diode (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, Californiamarker 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 than incandescent lamps 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 are depleted. By contrast, the output of a non-regulated flashlight changes proportionally to the voltage of the battery, resulting in a significant decline in output as battery capacity - and thus voltage - drops as the flashlight is used. 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 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 aluminum bodies act as a heatsink for the high-power LED. Very few high-output LED flashlights use a plastic body, since plastics do not conduct heat as well as metals.

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 two 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, 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) and are usually rather bulky. An example of an HID flashlight is the Surefire Hellfire Weaponlight.

Other designs

A fully-sealed disposable flashlight
headlamp is a flashlight worn on the head.

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.

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. In a disposable flashlight, when the batteries are depleted or the bulb fails, the entire product is thrown away or recycled and a new one purchased to replace it.

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



References

  1. Patent number: 617592 by David Misell
  2. History of Batteries (and other things)
  3. Flishlight Museum
  4. Using Gun Lights



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