National Flashlight Day takes place on December 21, 2021. It is held on Winter Solstice, which is the longest night of the year. Therefore a flashlight is a useful tool on this day. A flashlight is a hand-held portable electric-powered light source. Usually the light source is a small incandescent light bulb or light-emitting diode.
The invention of the dry cell and miniature incandescent electric light bulbs made the first battery-powered flashlights possible around 1899. Today flashlights use mostly incandescent lamps or light-emitting diodes and run on disposable or rechargeable batteries. Some are powered by the user turning a crank or shaking the lamp, and some have solar panels to recharge a battery.
In addition to the general-purpose hand-held flashlight, many forms have been adapted for special uses. Head or helmet-mounted flashlights designed for miners and campers leave the hands free. Some flashlights can be used underwater or in flammable atmospheres. (With material from: Wikipedia)