This paper describes how a flashlight works. A portable hand held electric device which provides light is commonly called a flashlight. The function of the flashlight is to provide a portable light source for use when stationary light sources are non-existent or inadequate. It is particularly useful in emergency situations and outdoors. Although flashlights come in many different forms, they are typically cylindrical in form with a lens at the light source end. It is comprised of seven essential parts. Each of these parts must be present to ensure the device will operate effectively. However, for the purposes of this paper, the focus will be on the switch, the contacts, the case, the light source, and the reflector; keeping in mind that all flashlights must also have a battery or batteries to power the device as well as some type of lens to protect the light source.
¶ … appearance, and a list of parts. It also contains a description for each part individually including a definition, function, appearance, and link to the next part. In conclusion it contains a summary of the function of flashlight and its components.
Mechanism Description
A portable hand held electric device which provides light is commonly called a flashlight. The function of the flashlight is to provide a portable light source for use when stationary light sources are non-existent or inadequate. It is particularly useful in emergency situations and outdoors. Although flashlights come in many different forms, they are typically cylindrical in form with a lens at the light source end. It is comprised of seven essential parts. Each of these parts must be present to ensure the device will operate effectively. However, for the purposes of this paper, the focus will be on the switch, the contacts, the case, the light source, and the reflector; keeping in mind that all flashlights must also have a battery or batteries to power the device as well as some type of lens to protect the light source.
The case of the flashlight is usually a cylindrical design. It may be designed so that it is completely disposable and both ends are sealed or, one or both ends may be removable to allow for battery replacement or bulb replacement. If the mechanism does not allow for replacement parts because it is a sealed device, it is referred to as a "disposable" flashlight and it may take many shapes.
The non-disposable flashlight typically takes a cylindrical form which is usually comprised of some type of plastic or metal, but the first flashlights were made with pasteboard according to the patent [1]. To ensure durability, the "plastic" now employed is generally some type of extremely strong polymer. Typically, the bottom of the cylinder is now sealed and the top screws off. The bottom part of the tube is usually the circumference of the size of the battery to be inserted into it. The length of the tube varies depending on the number of batteries to be inserted into the tube. Additionally, the switch of the flashlight is usually on the tubular case which holds the batteries, but it may be placed elsewhere. The head of the flashlight case is usually a slight bit larger than the tube that holds the batteries and it holds the lamp along with the reflector and the lens and it screws onto the threaded battery tube . They come in a multitude of colors, designs, materials, and sizes, but are generally as described above.
The inventor of the flashlight, David Misell, described the casing as follows: "the casing is a cylindrical tube, being shaped somewhat like a policeman's club, and is shown as formed of pasteboard. There is a bull's-eye at one end, consisting of a lens and a parabolic reflector" [1]. The shape of the mechanism described by the inventor of the device has remained consistent for over one hundred years, thus, attesting to its utility.
In order to power the light source, the batteries must connect to one another, the switch, and the light source. The mechanisms which enable this to occur are referred to as contacts. Going with the premise that this is a standard cylindrical flashlight, the contacts are generally comprised of thin strips of metal which are usually copper or brass copper and/or springs [2]. These contacts work in concert to conduct the electricity required to operate the flashlight.
"The electric connections are made as follows: One pole of the battery is connected to the button on the lamp. The other pole of the battery is connected to a metallic cover for the rear end of the casing, which is provided with a contact spring, soldered inside of the cover. This cover fits over a metallic band, which surrounds the casing and which is connected to a wire, leading therefrom to a metallic ring, forming a contact. The threaded band of the socket of the lamp is connected through the reflector and wire to the band, which surrounds the casing, and is placed close to the ring, so that the latter can be brought in contact therewith, thus closing the circuit through the lamp and the battery. The ring is normally held out of contact with the band by means of a spring and must be pressed in contact against the force of this spring. The ring is a convenient thumb-contact" [1]. Though this is the construction of the contacts contained in the original patent, it works essentially the same to this day.
The switch on the common flashlight no longer requires constant pressure to operate the mechanism on most flashlights. In fact, numerous switches now exist such as the slide switch, the "rocker," and the pushbutton [3]. These are the most commonly used switches on modern flashlights. Though they function slightly differently the general function of a switch is to open and close a circuit. To achieve this end, "there are two main components of any type of rocker switch. The first component is an actuator, mounted on an axis that allows it to rotate back and forth. An actuator is the part of a switch that moves and applies force to the contacts to turn the switch on or off. The second component of the rocker switch is the set of contacts. The state of the contacts determines whether the switch is set to on or off" [4]. When the contacts are touching, they are in the closed position which means that the device is "on." When the contacts are in the open position, the circuit is broken and the flashlight is in the "off" mode.
There are a number of different types of light sources that are now utilized in flashlights including LEDs, fluorescent, and incandescent light sources. However, "incandescent bulbs are the most common light source used in flashlights. These consist of a metal filament sealed in a glass bulb. When the filament is exposed to an electric current the resistance of the wire causes it to heat up and emit light in the visible wavelengths. The filament is welded to two wires that pass through holes in a cylindrical glass bead that forms the base of the bulb. This structure is placed in a fixture and a cylindrical glass envelope that is closed at one end is placed over the filament. The open end of the glass envelope rests against the glass bead. The structure is placed inside a vacuum chamber and heat is applied to seal the glass envelope to the bead. The heat causes the glass to soften, and may cause the filament to be displaced to one side. Therefore, care must be taken to ensure the filament is properly aligned or the bulb will not project a beam of light in the right direction" [5]. The end result is a device which resembles some flower bulbs.
"Other possible light sources include fluorescent bulbs, which are often used in camping lanterns. These bulbs emit light due to the excitation of gas molecules inside the bulb. LEDs, or light emitting diodes, are used in some specialty lights; these emit light when exposed to extremely low levels of electric current" [5].
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