flashlight
A flashlight is a small, mobile light source with its own energy supply . The name came about because most flashlights are small enough to be stowed in a pocket .
The flashlight was invented in 1899 by the Englishman David Misell , who sold the patent to the American Electrical Novelty and Manufacturing Company (now known as Energizer ). In Germany, Paul Schmidt received a patent for a battery-operated flashlight that dates back to 1906. However, he invented this shortly after his dry battery , with flour as an electrolyte, in 1896.
Layout and function
Torches are lights of a special design. They serve as the environment for the actual light source, the lamp . Therefore the correct lighting term is pocket light .
A flashlight usually provides a narrow beam of light . The luminaire housing consists of an elongated, often cylindrical handle into which batteries or rechargeable batteries are inserted at the end by means of a screw or slide lock . In order to be able to use lamps with a higher luminous flux, several battery cells are connected in series, often two or four Mignon (size AA ) or micro cells ( AAA ). Baby ( C ) or mono cells ( D ) are often used for larger flashlights . Both primary cells and accumulators are used.
At the front end there is a transparent glass or plastic pane, with high-quality lamps usually specially coated glasses are used to increase the light transmission. The light source ( incandescent lamp or light-emitting diodes ) is located behind the pane , which in turn is surrounded by a parabolic mirror , the reflector , to increase the light intensity . In the case of simple lamps with light-emitting diodes, the reflector and the disk are usually not required, since a reflector and a focusing lens are already integrated in the diode housing. The mirror is made of metal or metal-coated plastic. For lamps with a single high-performance LED, optical systems based on total reflection are also used instead of a mirror . These optics are usually made of transparent plastic, very rarely also of high quality glass. The area around the lamp usually has a larger diameter than the handle, as a larger reflector allows the light to be more closely focused and thus a greater light range with the same light output. For incandescent lamps with better light yield , halogen lamps filled with the noble gases xenon , but above all krypton, are used, which inhibit the evaporation of the filament and increase the service life of the lamp. This means that the incandescent lamp can be operated at a higher output, which in some cases increases the light yield considerably, and still achieves acceptable operating times.
Flashlights with plastic housings require electrical cables between the power source , switch and light source; with metal housings, this is often used as one of the conductors . One pole of the power source touches the light source directly and the other touches the housing, which is connected to the second connection of the lamp socket via a switch.
Quality features
Cheap flashlights are often not break-proof, the contacts corrode in humid air or from battery fluids, the reflector is incorrectly shaped, the lamps require a lot of energy, but at the same time emit little light. The metal parts often have poor contact with one another. An essential quality feature is the design of the on / off switch.
The photometric performance data, such as the luminous flux , measured in lumens , or the color temperature , measured in Kelvin , are not specified regularly. Existing information, in particular the range and duration of the light with a set of batteries, is in some cases incorrect.
When using an incandescent lamp as a light source, the light color changes as the voltage of the cells decreases due to the discharge during operation, while the brightness decreases. When using LEDs, the light color does not usually change noticeably, only the brightness decreases. While incandescent lamps initially get darker when the batteries are discharged and soon go out completely, many LED lamps can continue to shine with low brightness for a long time. At the end of the discharge, the brightness is often less than one percent of the brightness with fresh batteries. Some manufacturers use this to indicate a lighting duration of several hundred hours per battery set, without mentioning that the light output can still be used at this point in time, but is several orders of magnitude below the advertised maximum output. Torches with electronic stabilization of brightness by regulating the lamp voltage (incandescent lamps) or the lamp current (LEDs) are not offered in the lower price categories.
Embodiments
Simple flashlights are usually manufactured from plastic using an injection molding process and assembled in a bag-like manner. There are also flashlights whose body consists of a sheet metal tube. Plastic lamps are widespread and are also distributed as promotional gifts, but if they are well made, they can have the same practical value as metal lamps. Their main advantages are their lower weight and price.
Flashlights made from metal turned parts are usually of higher quality and mechanically more resilient than plastic lamps, but they are also correspondingly more expensive to purchase.
The batteries in the handle serve as a power source for the light source. The most common ways of switching the lamps on and off are a rotatable lamp head or a switch embedded in the handle .
In some models, the light source is attached to the handle part of the lamp, while the surrounding mirror is attached to the rotatable head of the lamp. By turning the head, it is often possible to focus the light source variably . For example, the beam can be set divergent in order to illuminate a larger area at the expense of the illuminance.
Possible uses
The possible uses for flashlights are extremely diverse. They range from the light source during a fuse change in the event of a power failure, to night hikes , camping tours and dives at greater depths. There are special lamp types for the individual areas, for example those with larger batteries for longer operating times or waterproof lamps for diving. Flashlights are standard equipment for all types of rescue workers, security forces, fire departments and police .
Lamps for emergency lighting are often housed in wall brackets, which ensure both trickle charging and recharging for the battery. They light up as soon as they are removed.
In general, however, only relatively small areas can be illuminated with flashlights at a short distance. Headlights are required to illuminate larger areas .
Power supply
- Most of the time, the flashlights are powered by batteries or replaceable accumulators.
- Flashlights for the professional sector in particular have an integrated battery, which can be charged with a charger at the socket.
- Older dynamo flashlights without a battery shone as long as the generator was operated by alternately pressing against the spring pressure and opening the hand. Accumulators and batteries used to have a high self-discharge and were discharged at some point, even when not in use; a generator, on the other hand, is inexhaustible.
- Dynamo flashlights with rechargeable batteries are now available with LEDs in various more or less cheap versions; Cranking it for a few seconds is enough for a few minutes of lighting time.
- Induction coil: Here the flashlight contains a metal coil with an embedded magnet. An integrated battery or capacitor is charged by shaking. The advantage of this variant is the independence from a power source. However, the higher cost of charging can be a disadvantage; so it would make sense to use the battery z. B. to be able to charge with a power supply. In addition, the movement can damage the lamps because the filament can tear. Therefore, these flashlights should contain LEDs.
- Charging the battery using a solar cell has not really caught on, whereby the flashlight is placed in a strong light source such as sunlight during the day. In general, strong heat will shorten the battery life. Furthermore, depending on the weather, sunlight is not always available in sufficient quantities and is therefore not a reliable source of energy in this sense. The small area of solar cells leads to long charging times or reduces the power yield. (See also charger # solar modules with charge controller )
Special flashlights
In addition to conventional flashlights, there are also lamps that, in addition to a normal incandescent lamp, also have a small fluorescent lamp on the side of the handle , with the help of which light can be generated more effectively and thus a somewhat larger area can be illuminated. The power consumption of such lamps is relatively high, so that the batteries are exhausted more quickly when using the fluorescent tube. Cold cathode fluorescent tubes (CCFL) are also used. The light output of these lights is higher than that of LEDs, but the light bundling is lower.
Another often found extra is an orange flashing light, which is primarily intended as a warning, for example in the event of a car accident. Also compasses are partially incorporated, its correct functioning is questionable, however, in view of the power lines in the lamp and the resulting magnetic fields. For outdoor activities, e.g. B. mountaineering , camping or cave hikes are nowadays headlamps more and more popular. Compared to conventional flashlights, they have the advantage that both hands remain free when they are worn with a rubber band on the head. Often, headlamps are only or additionally equipped with LEDs in order to allow a burning time of up to 200 hours.
In the case of lights known as adventure lamps, very large and relatively large numbers of batteries or accumulators are often used in order to cover the greater demand for electricity or to increase the operating time. On the one hand, this increases the weight of the lamp and makes it larger and, on the other hand, leads to changes in the construction . Since many and large batteries make the handle too thick to hold the lamp in one hand, an additional plastic or metal bracket is attached to the top of the lamp instead.
There are also flashlights that work without batteries. These contain accumulators or double-layer capacitors as a power buffer , which are charged via solar cells or a generator . Depending on the construction, the generator is driven by shaking, cable pull or crank. Such flashlights mostly work with LEDs , since they require less electricity than conventional incandescent lamps ( gas discharge lamps can, however, in some cases achieve a similarly high degree of efficiency ).
Flashlights are also made explosion-proof , they can then be used in the vicinity of highly flammable substances or within flammable gas mixtures. An example of this are miner's lamps .
LED flashlights
The technology of the flashlight is currently being fundamentally changed due to the development of inexpensive white light-emitting diodes . The main advantages are the long service life of the light source, the insensitivity to impacts, the lower power consumption, the independence of the light color from the battery voltage and often a brightness that can be regulated over a wide range. Light-emitting diodes are now about five times as efficient as incandescent lamps. While incandescent lamps without mechanical stress last an average of a few 100 to a few 1000 hours until they fail completely, often significantly shorter in flashlights, a service life of more than 100,000 hours (11½ years) is now assumed for white LEDs when properly installed. The service life is the time it takes to drop to half the initial brightness, since a complete failure due to aging usually takes much longer. Since LEDs are also very insensitive to impacts compared to incandescent lamps, they do not have to be replaced during the life of a flashlight, unlike incandescent lamps. The reason for premature aging or complete failure of LEDs is usually an unsuitable power supply, excessive load and insufficient cooling. The lifespan of the LEDs is greatly reduced in the event of overload, the usable brightness can drop to half the initial brightness after significantly less than 1000 hours instead of the advertised 100,000, in some cases even after less than 100 hours. Inexpensive LEDs, such as those built into cheap flashlights, are often less resistant than LEDs from brand manufacturers. However, since a flashlight is usually rarely used, these aspects do not play a role in the design of inexpensive flashlights. Flashlights that are not used regularly (e.g. household emergency lamps) will never last 1000 hours, so it does not matter whether the LEDs are overloaded.
Inexpensive LED flashlights are usually constructed with plastic-coated light-emitting diodes, as they are also used in displays and as signal lamps. The plastic cover also serves as a lens for focusing the emitted light, so that, in contrast to models with incandescent lamps or high-performance LEDs, no separate optical system has to be installed to bundle the light. The light output with light-emitting diodes of this type is limited, however, since no efficient cooling can be implemented, as is necessary with higher power consumption. Manufacturers compensate for this by installing many light-emitting diodes in a common housing, but this is only possible to a limited extent due to the design and, compared to a lamp with a single high-performance illuminant and optics of comparable size, results in a more diffuse light output. These flashlights are especially suitable for use in the household and hobby, where no concentrated light output is necessary and a low purchase price is in the foreground. The development of such LED flashlights has now reached the limit of 200 individual LEDs. Since the lamp head then has a diameter of 11 cm, the shape of the lamp is reminiscent of a shower head.
High quality LED flashlights
Many manufacturers now offer high-quality LED flashlights, which are characterized by robust workmanship and high light output. The illustration on the right shows two extremes, which clearly show the possibilities that result from the use of light-emitting diodes: on the left an LED flashlight with 2200 lumens , on the right a very small model with 180 lumens of light output.
Light source: In contrast to cheaper LED flashlights, high-quality models usually have individual light-emitting diodes installed, which, however, due to their design, allow passive cooling and can therefore be much more powerful. Usually white light-emitting diodes with component ratings of 1, 3 or 5 watts are used. In some models, however, much more powerful light-emitting diodes with rated outputs of up to 30 watts are used. The most efficient available white LEDs currently achieve a light output of over 150 lm / W , even more efficient LEDs with over 200 lumens / watt have been announced (as of 07/2011). Flashlights that are equipped with Cree LEDs have a burn time of up to 100,000 hours (with at least 70% luminosity). The power consumption is 20–50% less than previous LEDs with the same luminosity. The article Light Sources contains a table with examples of the light output.
Lens: The transmission of the light output can be higher and more stable in the long term by using glass lenses ( UCL lenses ) in contrast to plastic lenses. A scratched plastic lens e.g. B. scatters the light beam unnecessarily in all directions and thus lowers the brightness of the usable light cone. One disadvantage is the higher risk of breakage - on the other hand, glass lenses are exchangeable, while plastic lenses are often firmly attached to the rest of the housing.
Housing: Flashlight housings can be designed for higher requirements and, for example, protected against penetrating moisture, sometimes also IPX8 (e.g. 30 minutes in 2 m water depth) or even more in the case of diving torches. Lamp housings made of anodized aluminum are more scratch-resistant and help dissipate heat, as is important with LED lamps above around 1 watt. Plastic housings are poor at dissipating heat to the outside and are therefore rarely used in high-performance flashlights. The term "tactical flashlight" is often used colloquially for lamps that are used by special forces, the military, the police or security services. Their housings are often designed to be particularly stable and martial. Sharp edges can be used as a tool (glass breaker) or weapon. Before the introduction of compact LED lamps, flashlights were used e.g. B. the brand Maglite depending on the situation as a baton replacement for the police. Some lamps can be placed on the end cap and then, by shining upwards at the ceiling, can provide light in a room. This mode of operation is often called "Tailstand".
Electronics: A correspondingly dimensioned driver module in the form of a constant current source enables the torch to be kept at a constant level of brightness over almost the entire battery life. Voltage converters integrated in the driver also enable the operation of an LED flashlight from the low voltage of a single AA or micro battery ( step-up ), or the variable use of any number of cells ( step-down ) in order to extend the running time. Temperature sensors in lamps automatically reduce the output in order to prevent defects due to overheating. Non-current-regulated flashlights only use the internal resistance of the battery to limit the current . The light-emitting diodes then run permanently above their specification with new batteries, which causes them to age prematurely due to overheating. In addition to this constant decrease in the maximum brightness, the brightness also depends on the charge level of the battery or accumulator. Further disadvantages are possible color changes, such as a green tint when the LED is operated above its specified maximum power, as well as a lack of deep discharge protection for battery cells. As a rule, such flashlights must not be operated with rechargeable batteries anyway, as these have a lower internal resistance than alkaline-manganese batteries.
Operating concept: With the classic flashlight design, the power button is often on the front end of the shaft - the operation is similar to that of a hi-fi remote control. With smaller lamps, the switch is often attached to the end of the lamp and is operated like a ballpoint pen. Turning the lamp head is also a switch variant. The term "instant light" is used for the ability of a lamp to emit light by lightly pressing the switch and to go out again when the switch is released.
Switching levels / functions: More and more flashlights can not only be switched on and off, but also have other functions, e.g. B. adjusting the brightness in several stages. In addition, you can often find an SOS and various strobe functions . With a locator flash, the lamp flashes weakly every few seconds so that it can also be found in the dark. Some models also have changeable colors. The different modes are often changed by specifically pressing the power button, which is pressed halfway or fully ( clicky ). Some flashlights have a USB port that can be used to program user-defined functions.
The glare effect of strong lamps can significantly reduce eyesight, so that an orientation z. B. becomes difficult or impossible in traffic. This is because objects illuminated with the flashlight reflect the light back into the eyes and the pupils thus narrow, see adaptation . The effect is particularly strong with eyes that have previously been adapted to the darkness. In addition, there is a sometimes strong surprise effect in the event of unexpected glare.
Others
In the USA, the "National Flashlight Day" is celebrated on December 21st.
Web links
Individual evidence
- ↑ US Patent 617592
- ↑ Stiftung Warentest: Pocket and Headlights - Only 5 are good. in: test. 01/2006 (accessed online on February 4, 2013)
- ↑ Measurements of the light output of different LEDs over the operating time with different loads. ( Memento from April 28, 2010 in the Internet Archive )
- ↑ Test of various LED flashlights. Accessed December 30, 2014.
- ↑ 30-watt LED from Luminus. ( Memento from August 23, 2010 in the Internet Archive )
- ↑ Press release Cree Inc .: Cree achieves 231 lumens per watt in the laboratory. ( Memento from July 16, 2011 in the Internet Archive ) May 9, 2011.
- ↑ Cree LED Flashlight. Accessed January 21, 2013.
- ↑ Safe handling of high-performance LEDs - Federal Institute for Occupational Safety and Health ( Memento from December 5, 2011 in the Internet Archive )
- ↑ Timo Lokoschat : It's getting tight on the calendar. 365 strange commemorative and public holidays. Sanssouci , Munich 2010, ISBN 978-3-8363-0218-0 , p. 201.
- ↑ Day of the Flashlight at kuriose-feiertage.de