Mechanically-powered Flashlight - Shake Type Design

Shake Type Design

The linear induction or Faraday flashlight or "shake flashlight" is another design of a mechanically powered flashlight. It has been sold in the US beginning with direct marketing campaigns in 2002.

This design contains a linear electrical generator which charges a batterylike ultracapacitor when the flashlight is shaken lengthwise. The battery or capacitor powers a white LED lamp. The linear generator consists of a sliding rare earth magnet which moves back and forth through the center of a solenoid, a coil of copper wire, when it is shaken. A current is induced in the loops of wire by Faraday's law of induction each time the magnet slides through, which charges the capacitor.

An ultra-capacitor is used instead of a rechargeable battery since it doesn't wear out like a battery. This, along with the long-life LED lamp which doesn't burn out like an incandescent bulb, can give the flashlight a long lifetime, making it a useful emergency light. A disadvantage of many current models is that the ultracapacitor can't store much energy, limiting the operating time per charge. In most designs, vigorously shaking the light for about thirty seconds may provide up to five minutes of light, though the light may become dim after 2 or 3 minutes. Shaking the unit for 10 to 15 seconds every 2 or 3 minutes as necessary permits the device to be used continuously. It is often viewed as a toy, or an emergency backup for other flashlights.