Flashlight

Green flashlight

"Flashlight" is the NATO designation for the Yakovlev Yak-25 Soviet military jet.

A flashlight or torch is a hand-held portable electric spotlight. It is known as a flashlight mainly in the United States and Canada and as a torch in most Commonwealth countries.

A typical flashlight consists of a small electric lightbulb 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. The batteries in the first ones were of such short useful life that the common method of operating them was to flash them just long enough to discern the environs, and only as needed; hence the term "flash-light".

File:Incandescent flashlight spectrum.gif

The spectrum of an incandescent bulb type flashlight.

Recently, flashlights which use light-emitting diodes (LEDs) instead of conventional lightbulbs have become available. LEDs are far more efficient, and use less power than normal lightbulbs. Such torches have longer battery lifetimes. LEDs also survive sharp blows that often break conventional lightbulbs. A common misconception about LED-based flashlights is that they generate no heat. While this is generally true for lower-end flashlights, more powerful LED lights do generate significant amounts of heat.

Another innovation in flashlight design is the headlamp, 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.

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 that exists now in 2004 consists of a few LEDs with a switch, designed to be an endcap for a 9-volt battery.

High-quality flashlights go for as much as several hundreds of dollars. Such flashlights are very advanced, using special batteries, have adjustable brightness levels, dive-depth waterproof ratings, interchangeable optics, and are very bright.

Other power sources

Since batteries can be a burdensome cost in developed countries, let alone in the third world, the development of self-powered torches is a welcome advance. Some use solar panels to recharge their batteries during the day.

The clockwork torch has a spring with a winding handle, which powers the torch for a period of time.

Some flashlights have an electrical generator built into it. Dynamo-powered flashlights have a winding crank connected to a stepper motor 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. However, these types of flashlights have been reported to be ineffective because of the low energy.

External links

Manufacturer sites

Hobbyist sites

Other power sources

See also

External links

Manufacturer sites

Hobbyist sites