Flashlight

A flashlight is a small, portable light source with its own power supply. The name arose because most flashlights are small enough to be stowed in a pocket can.

The flashlight was invented in 1899 by the Englishman David Misell who sold the patent to the company American Electrical Novelty and Manufacturing Company (now known as Energizer ). In Germany Paul Schmidt received a patent for an electric torch, which dates back to the year 1906. He invented this, however, shortly after its dry battery with flour as an electrolyte, in 1896.

• 5.1 High-quality LED flashlights

Design and function

Flashlights are lights in a special design. They serve as an environment for the actual bulb, the lamp. Therefore, the light technically correct term is torch.

A flashlight usually provides a narrow cone of light. The luminaire housing consists of an elongated, often round handle, in the be used by means of a screw or sliding closure at the end or rechargeable batteries. In order to use lamps with a higher luminous flux, a plurality of battery cells are connected in series, often two or four AA - (AA) or micro cells ( AAA). For larger flashlights often (D ) are used Baby (C) or D-cells. Both primary cells and batteries are used.

At the front end is a transparent glass or plastic disk with high quality lamps specially coated glasses are usually used to increase the light transmittance. Behind the disc is the light source ( light bulb or light emitting diodes ), which in turn includes the optimum luminous efficiency of a parabolic mirror, the reflector. The reflector and the disk accounts for simple low power LED lamps mostly, as there is a reflector and a focusing lens are already integrated into the diode housing. The mirror is made of metal or metal -coated plastic. In lamps with a single high-power LED and optical systems can be used instead of a mirror, which is based on total reflection. These lenses are usually made ​​of transparent plastic, very rarely made ​​from high quality glass. Normally, the area around the bulb has a larger diameter than the handle, since a larger reflector allows for closer focusing of the light and thus a higher light range with the same light output. For incandescent lamps with better light output but mainly krypton -filled halogen bulbs are the noble gases xenon, used to inhibit the evaporation of the filament and increase the life of the bulb. Thus, the filament lamp can be operated at higher power, which greatly increases the efficiency to some extent, and still achieve acceptable operating lives.

With flashlights with plastic housing electrical cables are required between the power source, switch and light source in metal housings this is often used by itself as one of the leaders. The current source having one terminal directly touches the light source and the other the casing which is connected via a switch to the second terminal of the lamp socket.

Quality characteristics

Cheap flashlights are often not unbreakable, the contacts corrode in moist air or battery fluids, the reflector is incorrectly formed, the lamps consume a lot of energy and give little light. Often, the metal parts have poor contact with each other, so that the lamp provides very little light.

The photometric performance data such as the luminous flux, measured in lumens or light color, measured in Kelvin are given at the least flashlights. Existing information, especially the beam width and the burn time with one set of batteries, are often greatly exaggerated. When using a light bulb as the light source, the light color with decreasing voltage of the cells by the discharge during operation varies greatly, while the brightness decreases. When using LEDs, the light color usually does not change appreciably, only decreases the brightness. While incandescent bulbs when the batteries are discharged, are initially dark and pretty soon go out completely, many LED lamps can long continue to light with low brightness. The brightness is at the end of the discharge often less than one percent of the brightness with fresh batteries. Some manufacturers use this to print an extremely long burn time of several hundred hours per Batterisatz on the packaging, without mentioning that the light output at this time is indeed still available, but several orders of magnitude less than the advertised maximum power. Flashlights with electronic stabilization of the brightness by adjusting the lamp voltage (incandescent ) or the lamp current (LEDs) are not available in the lower price ranges.

Embodiments

Simple flashlights are usually made from injection molded plastic and assembled in the bag construction. Similarly, there are flashlights, whose body consists of a sheet metal tube. Plastic lamps are widely used and distributed as a giveaway, but can in good processing just such a use value have as metal lamps. Their advantages are mainly in the lower weight and price.

Flashlights made ​​of metal turned parts are usually superior and mechanically stronger than plastic lamps, but also correspondingly more expensive to buy.

The batteries in the handle of the light source serving as a power source. The most common variants to the lamps on and off are a rotatable head lamp or a recessed grip switch.

The light source is fixed in some models on the grip portion of the lamp, while the surrounding mirror is mounted on the rotatable head of the lamp. Thus, by turning the head often a variable focusing of the lamp possible. For example, the beam can be divergent set to illuminate at the expense of intensity of a larger area.

Purpose

The uses for flashlights are extremely diverse. They range from light dispenser during a fuse, a power failure overnight hikes, camping trips to deeper dives. There exist for each area special lamp types, such as those with larger batteries for longer usage or waterproof lamps for diving. For all kinds of emergency services, security forces, fire and police departments include flashlights as standard.

Lamps for emergency lighting are often housed in wall mounts that at the same time ensure the maintenance charging and recharging of the battery. They light up as soon as they are removed.

In general, only relatively small areas can be illuminated at a short distance with flashlights, however. In order to illuminate larger areas, headlights are required.

Power supply

• Most of the flashlights are powered by batteries.
• Especially professional flashlights have a built-in battery that can be recharged from a wall outlet with a charger.
• Dynamo flashlight without battery were to incandescent times, the only reliable source of light. The shone lamp, as long as you operated the generator by pressing against spring pressure and open the hand. Rechargeable batteries sooner had a high self-discharge, and are eventually discharged and during use, a generator is inexhaustible.
• Dynamo Flashlight with battery there today with LEDs in various more or less cheap versions, a few minutes of cranking enough for a few minutes burn time.
• Induction coil: Here the flashlight includes a metal coil with embedded magnets. By shaking an integrated battery or capacitor is thereby charged. Advantage of this method is its independence from a power source. However, a disadvantage is the higher cost for charging be, so it would be useful to be able to charge the battery, for example, with a power supply. In addition, the bulbs can be damaged by the movement, since the wire may break, so these flashlights should include LEDs.
• Not yet enforced has the charge by means of a solar cell, the flashlight in a strong light source such as sunlight during the day down. Due to the solar cell, a battery while charging. Again, we recommend a second power source.

Special Torches

In addition to conventional flashlights still exist lamps that still have other than a normal light bulb in the side handle a small fluorescent lamp that will help generate more effective light and consequently a slightly larger area can be illuminated. The power consumption of such lamps is relatively high, so that the batteries are depleted faster when using the fluorescent tube. There will also be cold cathode fluorescent tube (CCFL) used. The luminous efficacy of this lamp is higher than that of LEDs, the light - bundling but less.

Another commonly found Extra is an orange flashing light, which is mainly as a warning, for example in car accidents, thought. Also compasses are partially built, but its correct functioning is questionable in view of the power lines in the lamp and the resulting magnetic fields. For outdoor activities, such as mountain climbing, camping or cave- hiking today find headlamps at an increasing rate. Compared to conventional flashlights they have the advantage that remain free by wearing a rubber band on the head with both hands. Often headlamps are only or additionally equipped with LEDs, so as to allow a burn time of up to 200 hours.

When designated as an adventure lamps lights often very large and relatively many batteries are to meet the greater demand for electricity or to increase the operating time used. On the one hand increases the weight of the lamp and make them larger, and on the other hand leads to changes in the construction. Since the handle by many and large batteries is too thick in order to keep the lamp in one hand, an additional plastic or metal clip attaches to the top of the lamp thereto instead.

There are also flashlights that work without batteries. These included as a current buffer battery or double-layer capacitors, which are charged via solar panels or a generator. Depending on the design of the generator is driven by shaking, cable or crank. Such flashlights usually work with LEDs, as they require less electricity than conventional incandescent lamps (gas discharge lamps may, however, partly a similarly high efficiency reach ).

Flashlights also be made explosion-proof, they can then be used near flammable materials or within flammable gas mixtures. An example of this are miner's lamps.

LED flashlights

The technique of the flashlight is fundamentally changed by the current development of cheaper white LEDs. Major advantages are the long life of the light bulb, the insensitivity to shocks, lower power consumption, the independence of the light color of the battery voltage and often an adjustable over a wide range of brightness. LEDs are now reaching approximately five times the efficiency of incandescent lamps. While incandescent lamps without mechanical load last an average of some 100 to some 1000 hours to total failure, in flashlights often significantly shorter in white LEDs now with proper obstruction a lifespan of more than 100,000 hours ( 11 ½ years ) is assumed. The life of this time is referred to sink to half the initial brightness, since a complete failure due to aging usually takes much longer. Since LEDs also compared to incandescent lamps are very susceptible to shock, they do not need to be renewed in contrast to incandescent lamps during the life of a flashlight. Reason for a premature aging or a complete failure of LEDs is usually inadequate power supply, load too high and inadequate cooling. The service life of LEDs falls off rapidly in case of overload, the usable brightness case of severe congestion after significantly less than 1000 hours instead of the advertised 100,000 decrease to half the initial brightness, sometimes even after less than 100 hours. Cheap LEDs, similar to those installed in cheap flashlights, here are often less resistant than LEDs from brand manufacturers. As a flashlight but is usually seldom used, these aspects play no role in the design cheaper flashlights. Do not regularly used flashlights (eg emergency lamp in the household) will probably never reach 1000 hours of time so that it may be the manufacturers care if the LEDs are overloaded.

Cost-effective LED flashlights are mostly constructed with a plastic-coated LEDs, as they also come in displays and as a signal lamp for use. The plastic sheath serves simultaneously as a lens for focusing the emitted light, so that in contrast to models with incandescent or high-power LED, no separate optical system for focusing the light needs to be installed. The light output with LEDs of this building type is limited, however, since no efficient cooling can be realized as it is necessary for higher power capacity. The manufacturers compensate for this by spoil many LEDs in a common housing, which, however, due to the design is very limited and, compared to a lamp with a single high-power light source and an optical system of comparable size, resulting in a more diffuse light output. These flashlights are especially suitable for use in household and hobby where no concentrated light output is necessary and a favorable purchase price is in the foreground. The development of such LED Flashlight has reached the limit of 200 individual LEDs. As the lamp head then has a diameter of 11cm, reminds the lamp shape to a shower head.

High-quality LED flashlights

Meanwhile, many manufacturers offer high-quality LED flashlights, which are characterized by their sturdy design and high light output. The figure on the right shows two extremes, where it is clear what opportunities arise through the use of LEDs: Left LED flashlight with 2200 lumens, right a very small model with 180 lumens of light output.

Bulb: Unlike less expensive LED flashlights are installed individual light-emitting diodes for high-quality models in general, but due to their design allow for passive cooling and thus can be much more powerful. Most white LEDs are used with component power ratings of 1, 3 or 5 watts. In some models, but also far more powerful LEDs are rated up to 30 watts used. The most efficient available white LEDs are currently achieving a luminous efficacy of 150 lm / W, more efficient LEDs with 200 lumens / watt are announced ( 07/ 2011). Flashlights that are equipped with Cree LEDs, have a burn time of up to 100,000 hours ( at least 70 % luminosity). The power consumption is at the same luminosity 20-50 % below the previous LEDs. The article light sources includes a table with examples of the light yield.

Lens: The transmission of the light output can be higher and long-term stability through the use of glass lenses ( UCL lenses ) as opposed to plastic lenses. A scratched plastic lens, for example, scatters the light beam unnecessarily in all directions and thus lowers the brightness of the usable light cone. A disadvantage is the increased risk of fracture - on the other hand, glass lenses are interchangeable, while plastic lenses are often fixedly connected to the rest of the housing.

Housing: flashlight casing can be designed for higher standards and protected against moisture penetration, for example, sometimes IPX8 (eg, 30 minutes in 2 m water depth) or in the case of dive lights even more. Lamp housing made of anodized aluminum are scratch resistant and assist in heat dissipation as above about 1 watt is important in LED lamps. Plastic housing conduct heat poorly to the outside and are therefore rarely used in high-performance flashlights.

Electronics: An appropriately sized driver block in the form of a constant current source provides a constant brightness of the flashlight over approximately the entire battery life. In the driver built-in voltage converter also allow the operation of an LED flashlight from the low voltage of a single Mignon or Micro batteries ( Step-Up ), or the variable use of multiple arbitrary cells ( step-down ) to extend the term. Temperature sensors in lamps automatically reduce the power to prevent a failure due to overheating. Non- current regulated flashlights use for current limiting only the internal resistance of the battery. The LEDs then run with new batteries permanently above its specification, which makes them age prematurely due to overheating. In addition to this steady decrease of the maximum brightness, the brightness of the charge state of the battery or the battery is also dependent. Other disadvantages are the possible color changes, such as a green tint when the LED is operated above its predetermined maximum power, and a lack of protection against total discharge of the battery cells. Typically, these flashlights should not be operated with batteries anyway, as these than alkaline manganese batteries have a lower internal resistance.

Operating concept: flashlights available in Europe have the power button often at the front end of the shaft - the operation is similar to a hi-fi remote control, in the U.S., the switch is often attached to the lamp end ( "American Style" ) and is operated as a pen.

Switching stages / functions: More and more flashlights can not only be switched on and off, but have other functions, such as adjusting the light intensity in several stages. In addition, you can often find a SOS and various flash functions (English strobe). When a locator flash, the light will flash every few seconds on weak so that they are also found in the dark. Also have some models with replaceable colors. The different modes are often changed by the targeted clicking the on that is pushed through to semi- or fully ( Clicky ). Some flashlights have a USB port, you can program via the user-defined functions.

The strong glare lamps can significantly restrict the vision, so that an orientation, for example, difficult in traffic or impossible. This is because that reflect the flashlight is light objects the light back into the eyes and the pupils thus constrict, see adaptation. Particularly strong is the effect on previously adjusted to the dark eyes. There is also a strong part of surprise at unexpected glare.

Others

In the U.S., each committed on December 21, the "Day of the torch " ( "Flashlight Day" ).