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 or electromagnetic induction. It is known as a flashlight mainly in the United States and Canada and as a torch or electric torch in most Commonwealth countries.
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.
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.
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, CA, 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.
A common misconception about LED-based flashlights is that they generate no heat. 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.
Some advantages of this design are that they produce more light than an incandescent flashlight using the same amount of electricity, and the bulb will last a longer time and is more shock resistant than a regular incandescent bulb. However, they are more expensive and are usually rather bulky. An example of an HID flashlight is the Surefire Hellfire Weaponlight.
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. It is possible that future developments of battery and LED technology will bring interesting new designs. For instance, one very small light consists of a few LEDs with a switch, designed to be an endcap for a 9-volt battery.
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. As a unique example of a high end manufacturer, with non-cylindrical, unique design, Lumencraft was one of the first manufacturer to create designs that cater more towards a higher end design and art-conscious market rather than the tactical military and law enforcement markets.
Since batteries can be a burdensome cost in developed countries, let alone in the third world, the development of self-powered flashlights is a welcome advance. Some use solar panels to recharge their batteries during the day.
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.