Flashlight

Fast history

October 21st, 1879: Thomas Alva Edison designs a lamp whose filament is a carbonized bamboo filament.
A long time, the incandescent lamps will use a carbon filament.
the modern lamps use the Tungstène.
the cap bayonet is invented by Swan, in competition with the screw base of Edison.

The incandescent lamps often have a collected and rebounded form, but can be lengthened (linolite).

The fluorescent Tube used for lighting and the luminous Enseigne S is generally linear, but at the end of the 20th century, this technology evolved/moved by allowing the manufacture of various forms, more compact, integrating a food electronic and being able to replace the incandescent lamps.

There exist also now lamps made up of electroluminescent diodes, they are used for lighting only since the beginning of the 21e century.

Classification of the lamps

The flashlights use various physical phenomena to produce light starting from electricity:

the Incandescence;
the Fluorescence;
the electroluminescence;
the Chimiluminescence which does not produce yet a light in the form of lamp;

Other modes of production of light are not currently usable for lighting; so they do not give place currently to any industrial production

the Luminescence caused by other causes but electricity;
the Phosphorescence;
the Triboluminescence;
the Bioluminescence.

Incandescence

Traditional incandescent lamp

Lamp with halogens

Lamp with nanotubes

It functions like models it traditional, but one replaced the tungsten filament there by a Nanotube in Carbone. Developed in 2004 by Enquiring S Chinese directed by Jinquan Wei, it has the advantage of emitting more light at equal power. A marketing is considered as of 2009. ()

Defects

To each lighting of the lamp, the filament is subjected to an overheating, the intensity of the electric current being higher in the cold filament, for this reason the lamps roast most of the time at the time of lighting.

The filament slowly evaporates with the wire of the hours spent in a state close to fusion, it is thus thinned and ended up melting with a lighting or breaking with the first important shock. Another effect, the gases resulting from the evaporation of the filament while condensing on the bulb, blacken glass gradually, thus decreasing the quantity of light produced by the lamp.

Another large defect: only 5% of electrical energy are used for lighting… and 95% to heat (see Apparent brightness) (glass of an incandescent lamp 230 volts under tension is located at the neighborhoods of 300 °C; attention thus not to pose neither fabric, neither paperboard, neither paper, nor wood… directly on glass under penalty of fire hazard).

Sources with glow discharge under low pressure

The sources with discharges produce light thanks to a gas or a slightly ionized vapor (except for the lamps with sodium), a plasma. The pressure of filling varies few millibars with several tens of millibars and the powers dissipated per unit of length are relatively low. This characteristic imposes lamps of relatively large size. Tested in 1869 by Louis Becquerel, they gather:

fluorescent lamps with mercury vapor;
the lamps sodium vapor low pressure;
the fluorescent tubes improperly called “neons”.

These lamps have a much better output than the sources with incandescence, although they are associated with a complex equipment, variable according to gases used for their implementation.

Fluorescent lamps

The principle of operation is the following:

a Electric shock through a Gas made up of a mixture of vapor of mercury and of a noble Gas, produces a ultraviolet Rayonnement.
This light, nonexploitable directly with an aim of lighting, is absorbed by a fluorescent Poudre recovering the internal wall of the bulb of glass
This powder restores luminous energy in the form of visible light.
the Température of color of the emitted light can be controlled on a very broad beach while making modifications in the composition of the fluorescent powder.

The value of output can reach up to 115 lumens by Watt for the fluorescent tubes with very high output.

These lamps present in various forms:

Tubular-linear: with thermoelectronic electrodes with emission at each end
Tubular-circular: with the electrodes connected to a common casing
Tubular-compact: whose tube with discharge is folded several times
Sphérique: whose electric shock is excited by an antenna radio frequency

Sodium vapor lamp

Negative glow lamps

These lamps present a case to share in the family of the sources under low pressure. The very short distance between their electrodes does not allow the complete development of the glow discharge. Only a luminous sheath, the negative gleam, develops around cathode. These lamps are generally very compact and dissipate low powers ranging between a half Watt and a few tens of milliwatts. They are often used as luminous witnesses (detection of current, tension or starting of a circuit).

There exist four types of negative glow lamps:

Neon lights (orange);
Lamps with neon-xenon with fluorescent coating (green, blue);
Lamps with argon (blue, ultraviolet);
Lamps with helium (pink);

Luminescent gas-discharge lamp under high pressure

These lamps have an internal pressure about the bar to ten bars. It results from it that the ionized gas responsible for the light output is much more brilliant and hot. Thus, of stronger powers can be dissipated in a space of a few centimetres. The first lamps of this type were created at the beginning of the 20th century and gather mainly:

mercury discharge lamps;
lamps with metal halides;
sodium vapor lamps high pressure.

For more specific uses there exists also of different types of sources:

lamps with xenon with long arc;
krypton lamps with long arc.

Arc lamps under very high pressure

Electroluminescent source with semiconductor

See also: Electroluminescent diode, Lamp with led

Composed of often several electroluminescent diodes high luminosity, one very important lifespan (50 000 hours) the lamps with diodes start to replace the incandescent lamps in portable lighting and for the Signalisation. Their still high cost, the need for the specific use of food electric (basic D.C. current tension) and their still modest luminous output (50 lm/W for the best sources) still limit their democratization vis-a-vis the lamps with filaments.

A Electroluminescent diode functions as follows:

At the time of the recombination of an electron and a hole in a semiconductor it can have there emission of a Photon.
the transition from an electron between the band of conduction and the valence band can be done with the conservation of the Vecteur of wave $\ vec {K}$ . It is then radiative (emissive) and it is accompanied by the emission of a photon.

Chemicoluminescence

In a plastic tube, a chemical Composé reacts to an action Mécanique, this phenomenon makes it possible to obtain a source of light of help (standard Snaplight).
Of objects (bracelets, collars, cerceaux, etc) decorative is used at the time of night festivals.
In criminology, the phenomenon makes it possible to highlight traces of blood little or not visible with the naked eye (in this case, the Luminol reacts with the Ion S Fer of the red globules, by producing light).

Applications

See too

Beats-smg: Alektrėnė lėmpele

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