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From the outside modern incandescent lamps still very much resemble the first Edison lamps but a lot of technical fine tuning had been made on the inside. In 1911 a filament made of wolfram had replaced the carbon filament. The precise origin of the name wolfram is unknown but it most probably is related to the name of the Irish chemist and
that the mineral wolframite might contain a previously undiscovered element. Instead of wolfram often the name tungsten is used, derived from the Swedish expression "tung sten" (heavy stone), a stony mineral of wolfram. From 1913 on the glass bulb was filled with argon or nitrogen in order to reduce the evaporation of the filament. The temperature of the filament can increase to about 2500 ºC, emitting heat as well as light (see infrared
incandescent lamps (see also IR radiators)
The invention of the incandescent lamp as we know it today, an electric current through a metal wire in a glass bulb without oxygen, is often attributed to Thomas Alva Edison. Edison however was only one of many technicians that contributed to the development of a practical method to generate light with help of electricity. In 1879 Joseph Wilson Swan build an electric lamp out of a vacuum glass bulb
improved this design and in 1880 he succeeded in producing a 16 Watt incandescent lamp with a carbon filament that burned for about 1500 hours continuously. Twenty-five years earlier however, in 1854, Heinrich Göbel already succeeded in the construction of a good performing incandescent lamp. This lamp had a
constructed from a bottle that was made vacuum with help of mercury. Göbel his lamp burned for about 400 hours. In 1879 Edison claimed a patent on a similar lamp but Göbel disputed this patent and in 1893, one year before he passed away, he finally got his rights. Because Edison in the end was the first one to succeed in the industrial production of incandescent lamps, he widely is accepted as the inventor of it.
filament of carbonised bamboo fibres and was
and a platinum filament that lasted a few hours. Thomas Alva Edison
tube-lights (see also ultraviolet radiators)
Tube-lights (TL) are the most commonly used sources of light for therapeutic use. They lack the disadvantage of a high heat production, as do incandescent- and high-pressure gas discharge
lamps. The working principle of tube-lights is based upon a combination of low-pressure mercury vapour discharge and fluorescence. A glass tube is covered at the inside with a fluorescensive coating and filled with a mix of mercury vapour, argon and krypton. With a sufficient high voltage between electrodes at both ends of the tube, a gas discharge will take place, activating the mercury vapour and causing the emission of ultraviolet rays (see ultraviolet emission). The fluorescensive coating will then convert the ultraviolet
radiation into light, the colour spectrum being determined by its chemical composition. For domestic use the composition of the fluorescensive coating is such that it will produce a tinted white light. For light therapies it is also blue light that is used because of its positive influence on the chemical processes on and just below the skin. Blue light for example is used for the treatment of new-born babies suffering from neonatal jaundice and for the treatment of some forms of acne, in the latter case often
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light emitting diodes
A light emitting diode (LED) is a semiconductor that emits a narrow-spectrum radiation when an electric current flows through it in the forward direction. This emission is a form of electroluminescence and the wavelength of the emitted radiation depends on the composition of the semiconductor material. It can be infrared, visible or near ultraviolet and its power consumption (typical 20 mW) is much lower
in a semiconductor material and the lifetime of a LED is just as long as that of a standard transistor, which easily can be a quarter of an age. Visible-spectrum LED's were developed from 1962 on in the main colours red, orange, yellow and green. It was only in the 1990's that production of effective blue, green-blue
became possible. This triggered the development of small, battery powered light boxes that can be worn permanently, mounted underneath a visor or a hat in order to fight for instance Seasonal Affective Disorder or SAD. The peak emission of this kind of devices often is between green and blue, which is around 500 nm.
consisting of glass tubes filled with carbon dioxide, was quite poor and had to be tenths of meters long to produce a sufficient amount of light. Application of the Moore-tubes therefore stayed limited to large rooms like churches and theatres. The tube-light as we still know it today was only introduced in 1935 by André Claude. Since the filament of a tube-light is relatively small compared to an incandescent lamp it dissipates less heat making it very usable for straight light therapies and for some specific forms of colour therapy.
allowing the filament to operate at even higher temperatures thus producing an extremely bright light. Relative to the amount of light they produce, incandescent lamps produce an even greater amount of infrared radiation. This is why most infrared radiators for therapeutic applications are based on the principal of an incandescent lamp. For
straight light therapies incandescent lamps are not very efficient unless the excess of heat can be expelled easily like in modern hand-held devices for local treatment. Incandescent lamps made of coloured glass or equipped with separate screen filters were also widely used for colour therapies (see also healing radiation).
mineralogist Peter Woulfe who came with the idea
emission). Nowadays also krypton may be used as a filling gas,
supplemented with red coloured tube-lights. Unlike an incandescent lamp a tube-light, or any other gas discharge lamp, is not connected to the line voltage directly but always in series with a dedicated start- and ballast circuit. The first experiments with low pressure gas discharge lamps date back to the midst of the 19th century. Well known are the experiments of Heinrich Geissler and Alexandre Becquerel. In 1898 it was Daniel McFarlan Moore who first succeeded in constructing suitable gas discharge lamps. The yield of his lamps,
than that of any incandescent lamp. Unlike incandescent bulbs, LED's do not have a filament and they do not get especially hot. Their light emission is solely caused by the movement of electrons
and white LED's
lasers (see also infrared radiators)
A laser (acronym for Light Amplification by Stimulated Emission of Radiation) produces a beam of monochromatic, coherent and collimated bundle of radiation. The exact wavelength of a laserbeam depends on the nature of the used medium and may vary from X-ray, ultraviolet, visible light, near- and far infrared to microwaves. Lasers operating in the visible part of the electromagnetic spectrum were used in early experiments with hair removal techniques. Green lasers are used in prostate surgery.