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 term flashlight is used mainly in the United States and Canada. In other English-speaking countries, the most 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.
The flashlight on the left uses an incandescent bulb, while the one on the right uses LEDs to give white, red, blue, and infrared light
Incandescent flashlights use incandescent light bulbs which consists of a glass bulb and a tungsten filament. The bulbs are under vacuum or filled with argon, krypton or xenon. Some high-power incandescent flashlight use a halogen lamp where the bulb contains trace of halogen such as iodine or bromine to improve the life and efficacy of the bulb.
Developments in light-emitting diodes (LED)s have made practical flashlights that use LEDs instead of conventional light bulbs. 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. 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 and use less energy than incandescent lamps. LED flashlights have longer battery lifetimes than incandescent lamps of comparable light output. LEDs are also less fragile than conventional glass lamps.
Some LED flashlights electronically regulate the voltage supplied to the LEDs to stabilize light output as the batteries discharge. By contrast, the light output of non-regulated flashlights declines as battery voltage declines. LEDs also have the advantage of maintaining nearly constant color temperature regardless of input voltage or current, while the color temperature of an incandescent bulb rapidly declines as the battery discharges. Regulated LED flashlights may also implement user-selectable levels of output appropriate to a task, for example, low light for reading a map and high output for checking a road sign. This would be difficult to do in an incandescent flashlight since efficacy of the lamp drops rapidly at low output.
LED flashlights may consume 1 watt or more from the battery, producing heat as well as light. Heat dissipation for the LED often dictates that LED flashlights have aluminum bodies to dissipate heat; they can become warm during use.
Light output from LED flashlights varies even more widely than for incandescent lights. "Keychain" type lamps operating on button batteries, or lights using a single 5 mm LED, may only produce a couple of lumens. Even a small LED flashlight operating on an AA cell but equipped with a power LED can emit 100 lumens. The most powerful LED flashlights produce more than one thousand lumens and may use multiple power LEDs.
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).
A penlight is a small, pen-sized flashlight, usually containing two AA batteries or AAA batteries. In some an incandescent light bulb has an integral lens that focuses the light, thus no reflector is built into the penlight. Others use incandescent bulbs mounted in reflectors, while LED lamps are becoming increasingly common. Low-cost units may be disposable with no provision for the user to replace batteries or bulbs, and are sometimes imprinted with advertising for promotional purposes.
An LED headlamp
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.
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 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 size and shape 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.
Main article: Mechanically powered flashlight
One type of dynamo-powered flashlight has a winding crank connected to a small electrical generator that charges a capacitor. 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. Such flashlights can be useful during an emergency, when utility power and batteries may not be available.