A mechanically powered flashlight is one of several varieties of flashlight

Flashlight

A flashlight is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode...

 that are powered by electricity generated by the muscle power of the user, so they do not need replacement of batteries, or recharging from an electrical source. The light source can be a miniature incandescent bulb, or a light-emitting diode

Light-emitting diode

A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

.

Different mechanical motions are used to generate the required power, such as squeezing a handle, winding a crank

Crank (mechanism)

A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...

, or turning or shaking the device itself. These flashlights can also be distinguished by the technique used to store the energy: a spring

Spring (device)

A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...

, a flywheel

Flywheel

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

, a battery

Battery (electricity)

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

 or a capacitor

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

.

A well-designed, well-made mechanical flashlight can be a reliable, robust tool for providing light in emergency situations. However, poor-quality and outright fake mechanical flashlights have been widely sold, tarnishing the reputation of the product category.

Dyno torch

A dyno torch is a flashlight

Flashlight

A flashlight is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode...

 or pocket torch which stores energy in a flywheel

Flywheel

A flywheel is a rotating mechanical device that is used to store rotational energy. Flywheels have a significant moment of inertia, and thus resist changes in rotational speed. The amount of energy stored in a flywheel is proportional to the square of its rotational speed...

. The user repeatedly squeezes a handle to spin a flywheel attached to a small dynamo, supplying electrical current to an incandescent bulb or light-emitting diode. Because electrical power is produced only when the handle is squeezed, a switch

Switch

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another....

 is not needed. The flywheel makes sure the light is fairly constant, despite the fact that the power supply (the squeezing) is intermittent. Dyno torches were very popular in Europe during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

because the electrical power supply to homes was not very reliable.

In an alternative design, the dynamo charges a rechargeable battery

Rechargeable battery

A rechargeable battery or storage battery is a group of one or more electrochemical cells. They are known as secondary cells because their electrochemical reactions are electrically reversible. Rechargeable batteries come in many different shapes and sizes, ranging anything from a button cell to...

 or a capacitor

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

, and may offer 15 minutes or more of illumination for 1 minute of charging. However, this version could be considered less reliable for emergency use because the battery will eventually fail and need replacement.

Dyno torch design

In the photo, the L-shaped handle has a gear rack

Rack and pinion

A rack and pinion is a type of linear actuator that comprises a pair of gears which convert rotational motion into linear motion. A circular gear called "the pinion" engages teeth on a linear "gear" bar called "the rack"; rotational motion applied to the pinion causes the rack to move, thereby...

, which spins the white step-up gear, which in turn spins the flywheel on which is mounted the dark grey magnet, seen on the lower left. The magnet induces an electrical current in the red copper winding, seen on the lower right. The current from the copper winding flows through an incandescent bulb filament (not shown). A spring and ratchet returns the handle to its original position after each engagement.

Shake type design

The linear induction or "shake flashlight" is another design of a mechanically-powered flashlight. It was sold in the US via direct marketing

Direct marketing

Direct marketing is a channel-agnostic form of advertising that allows businesses and nonprofits to communicate straight to the customer, with advertising techniques such as mobile messaging, email, interactive consumer websites, online display ads, fliers, catalog distribution, promotional...

 campaigns beginning in 2002.

This design contains a linear electrical generator

Electrical generator

In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...

 which charges a capacitor

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

 when the flashlight is shaken lengthwise. The battery or capacitor powers a high-intensity white LED

LEd

LEd is a TeX/LaTeX editing software working under Microsoft Windows. It is a freeware product....

 or LED array. In the linear generator, a sliding rare earth magnet moves back and forth through a solenoid

Solenoid

A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...

, a spool of copper wire. A current is induced in the loops of wire by Faraday's law of induction

Faraday's law of induction

Faraday's law of induction dates from the 1830s, and is a basic law of electromagnetism relating to the operating principles of transformers, inductors, and many types of electrical motors and generators...

 each time the magnet slides through, which is used to charge the capacitor.

In the best designs, vigorously shaking the light for about thirty seconds may provide up to five minutes of light, though only the first 2 or 3 minutes are very useful. Shaking the unit for 10 to 15 seconds every 2 or 3 minutes as necessary permits the device to be used continuously. An ultra-capacitor is used instead of a rechargeable battery since it doesn't wear out like a battery.

Note that fraudulent counterfeit versions of these flashlights have been sold, most of which incorporate thin lithium cells "hidden in plain sight." In some of those, the "magnet" is not a magnet (or the coil is not connected) and no electricity is generated when the device is shaken. These fraudulent flashlights eventually become useless, since their internal batteries cannot be recharged or replaced, and the case is often permanently glued shut.

Other functions

Some mechanically powered flashlights include other functions and features beyond just a source of light. For example, certain models may have additional special operating modes, such as flashing red or yellow lights that can serve as a caution or warning to other people that might see the light. Some models include a loud electronic siren

Siren (noisemaker)

A siren is a loud noise making device. Most modern ones are civil defense or air raid sirens, tornado sirens, or the sirens on emergency service vehicles such as ambulances, police cars and fire trucks. There are two general types: pneumatic and electronic....

 that can also help warn of danger, or assist in locating someone who is lost. There are also many models of mechanically powered flashlights that include a built-in AM

AM broadcasting

AM broadcasting is the process of radio broadcasting using amplitude modulation. AM was the first method of impressing sound on a radio signal and is still widely used today. Commercial and public AM broadcasting is carried out in the medium wave band world wide, and on long wave and short wave...

/FM

FM broadcasting

FM broadcasting is a broadcasting technology pioneered by Edwin Howard Armstrong which uses frequency modulation to provide high-fidelity sound over broadcast radio. The term "FM band" describes the "frequency band in which FM is used for broadcasting"...

, weather

NOAA Weather Radio All Hazards

NOAA Weather Radio All Hazards is a network of radio stations broadcasting continuous weather information directly from a nearby National Weather Service office. It is operated by the NWS, an agency of the National Oceanic and Atmospheric Administration within the United States Department of...

 or shortwave

Shortwave

Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...

 radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

.

The quality and long-term reliability of these devices vary over a wide range, from high-reliability mil-spec emergency equipment down to one-time-use non-repairable throwaways.

External links

• ElectronicCrafts.org: Homemade shakelight
• Instructables: A homemade solenoid type dyno torch inside a TicTac box.
• Die Goldcap-Dynamolampe (in German
  German language
  German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....
  
  ) — converting a dyno torch to LED operation with capacitor storage