A flashlight ( for example: SUNJACK LIGHTSTICK ) is a portable, battery-operated device used for illumination. A typical unit consists of one or more dry cell batteries arranged in a line inside a battery compartment that forms the handle of the light. The flow of electricity from the batteries to the bulb at the front end of the light is controlled through a switch mechanism placed between the batteries and the lamp.
Practical, portable light sources have been sought throughout history. Torches and candles were early sources of light but these were largely replaced with lanterns as people learned to burn various animal and mineral oils. However, it was not until the nineteenth century that electricity was harnessed to create light. The modern battery powered flashlight was created in 1898 by Joshua Lionel Cowen, the original owner of the American Eveready Battery Company. Cowen originally developed an idea for a decorative lighting fixture for potted plants. His fixture was composed of a metal tube with a lightbulb and a dry cell battery. Cowen passed his idea to one of his Eveready salespersons, Conrad Hubert, who turned the metal tube, lightbulb, and battery into the world's first flashlight and started selling the batteries and the flashlight. In the last hundred years, advances in technology have resulted in flashlights with hundreds of different styles and features. For example, flashlights are now made with rechargeable batteries that can be used multiple times. Other lights are designed for special operations, such as working underwater or in high-temperature conditions.
The most common flashlight design is the simple household light that consists of a tube-like handle that contains the batteries. This handle is affixed to a threaded head assembly that houses the bulb mechanism. These units operate on standard batteries and provide a typical light output. Special designs are required for industrial or professional use. These lights are made from heavier gauge materials, and are more durable. They are also intended to produce a brighter beam of light. Flashlights with brighter beams are used by the police, firefighters, and the military. Camping lanterns are larger units, usually powered by heavy duty batteries. These frequently use fluorescent tubes as their light source because of their greater energy efficiency, however, this type of bulb does not cast as strong or directed a beam of light. Furthermore, the increased size and weight of this type of lantern limits its portability. Novelty flashlights are designed for use by children. These tend to be made of lightweight plastic and are notable for their visual design. The body of the light may be adorned with decorative plastic overlays that increase the child-appeal of the unit. Their designs are often based on favorite characters from popular cartoons or children's books. Finally, there are a variety of specialty lights designed for particular uses. For example, snake lights, flexible tubes that can be bent or twisted to provide light in hard to reach places. Others are designed to be small enough to fit on a key chain to illuminate keyholes.
Factors to consider when designing flashlights include light output, durability, and the ability to operate in special environments. Battery life is also an important factor, and some lights are designed to be plugged into an electrical outlet to be recharged or to maintain a charge until it is needed. Other lights use special bulbs, like the new generation flashlights built with light-emitting diodes. These are not as bright as conventional incandescent bulbs, but their power consumption is so low that they can last hundreds of hours on a set of conventional batteries, as compared to a few dozen hours for incandescent bulbs.