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incandescent lamps (see also sources of light)
Raising the temperature of the filament of a conventional incandescent lamp well above the regular 2500 ºC can increase the production of ultraviolet radiation. The UV yield of such an incandescent lamp however, will still never be more than a few tenths of a percent. Sun-lamps based on conventional incandescent lamps never became succesful therefore with one possible exception. The Philips "Zonlichtlamp", introduced
principle of the first lamps was based upon a continues voltaic arc between two electrodes made out of pressed carbon powder thus giving it the name carbon-arc lamp or arc-lamp. Due to its very intense light however, this type of lamp was not very well suited for the lighting of small rooms. Arc-lamps therefore were primarily used as street lights, in lighthouses and searchlights and for the lighting of public areas and larger rooms. The electromagnetic
spectrum of an arc-lamp is extremely wide and its radiation extends from light till rays well into the infrared and the ultraviolet ranges. The arc is responsible for the ultraviolet radiation and the major part of the light while the glowing tips of the carbon rods add to the infrared part of the spectrum. For sun-lamp applications enriching the carbon rods with a little iron increased the emission of ultraviolet radiation. A disadvantage of carbon-arc lamps was the short life span of the carbon rods that had to be replaced every few hours. For this
reason carbon-arc lamps for lighting purposes became obsolete shortly after the introduction of the incandescent lamp although specialised carbon-arc lamps as for instance in film projectors remained operational until after WWII. For therapeutic use carbon-arc lamps first were applied in light baths and later on, until well
For centuries oil- and gas lamps had been the most important sources of artificial light when, around 1860, the first practical usable electric lamps appeared. The first successful attempts to produce light by means of electricity were made by Sir Humphry Davy at around 1805. He succeeded in maintaining a voltaic arc between two rods of charcoal that lasted a few minutes. Due to the lack of reliable sources of energy and proper material for the carbon rods it still took half a century however before this kind of lamps became commercially applicable. The
into the 1950's, as sun-lamps. Just as with a mercury vapour arc-lamp a carbon-arc lamp required a ballast in the form of a transformer, a coil or a resistor (see electrical circuits). Most of the times this ballast was integrated in the base of the lamp but sometimes the ballast, mostly a glowing Kanthal wire, also served as an infrared source.
distribution that resembled that of natural sunlight. This lamp was intended to be used for the illumination of stores and warehouses however and not for medical purposes. In fact sun-lamps that resemble incandescent lamps most often turn out to be mercury vapour discharge lamps protected by an additional outer bulb (like in the Philips Ultrasol) or they are blended lamps as will be described further on on this page.
mercury vapour discharge lamps
Much more effective than incandescent lamps are UV-sources based on the principle of gas discharge. Atoms from evaporated metals like mercury and sodium emit a significant amount of electromagnetic radiation when they return to their normal state after being exited by an electric current. For mercury the
wavelength of this radiation is within the range of the ultraviolet area (see ultraviolet emission). The first practical applicable gas discharge lamp was constructed in 1901 by Peter Cooper HewittPeter Cooper Hewitt constructed the first practical applicable gas discharge lamp in 1901. The greenish-blue colour of this low-pressure mercury vapour
discharge lamp limited its use for lighting purposes. The relatively high amount of emitted ultraviolet radiation however, made the lamp suitable for treatment of certain skin diseases. For therapeutic appliances high-pressure mercury vapour discharge lamps have proven to be the most effective. In order to avoid the bulb of such lamps from melting, their temperature and thus their
effectiveness had to be limited. Küch and Retschinsky, the former closely related to Hanau, solved this problem in 1906 with the use of quartz glass. This quartz glass had a melting temperature of about 1100 ºC instead of somewhere between 500 and 800 ºC like conventional glass. A negative characteristic for lighting purposes was the transparency of the quartz glass for ultraviolet radiation, requiring additional filtering. The very same characteristic however, made the quartz glass lamps very usable in sun-lamps. The yield of high-pressure
mercury vapour discharge lamps is about 20% UV-rays, 20% light and 60% IR-rays. The life span of the lamps is especially limited by the decreasing transparency of the glass over time. To prevent sun-lamps from emitting too much of the undesirable UV-C, often
an additional protection is added that is opaque for UV-C. In many cases this filter consists of an additional glass bulb that surrounds the discharge lamp itself. Sometimes the discharge lamp is equipped with a removable or adjustable UV-B filter to regulate the effect of the treatment. Due to the high working temperatures and the vulnerability of the lamps there are high demands for the construction of the armatures. Since a gas discharge lamp possess a negative temperature
through the lamp must be stabilised with a ballast circuit, for example a coil or a transformer. The ballast element is often situated in the base of the armature giving it the required stability. A cheaper solution is the use of quartz tubes as ballast whom than can serve as an infrared radiator as well.
In addition to a carbon arc- or a mercury vapour discharge lamp many sun-lamps are also equipped with an infrared radiator in
electric configuration. When the armature is equipped with a dedicated ballast for the ultraviolet radiator, independent use of both radiators is possible. In order to save cost and weight however, in most cases the infrared radiator also functions as a ballast for the ultraviolet radiator. This prevents the ultraviolet radiator from being operated in combination with the infrared radiator only.
order to approach the characteristics of natural sunlight even better. Most of such infrared devices consist of a quartz tube or a metal wired element but combinations with (infrared) incandescent lamps, metal tubulars or dull radiators also exist. With many of such combined devices it is possible to activate the infrared radiator only. Whether or not it is as well possible to activate the
tube-lights (see also sources of light)
Basically conventional tube-lights (TL) for lighting purposes are low-pressure mercury vapour discharge lamps that are coated at the inside with phosphorus powder. Through fluorescence this powder converts the ultraviolet radiation of the lamp into light of a colour which hue depends on the exact chemical structure of the coating. Leaving out the phosphorus coating and making the glass tube out of quartz glass instead of conventional glass gives a
relatively cheap ultraviolet radiator. The output of such a lamp however, is lower than that of a high-pressure mercury vapour discharge lamp and the wavelengths of the emitted ultraviolet rays are much shorter. By using a special coating again, the short waved radiation can be converted to wavelengths in the more effective longer ultraviolet areas. Sometimes an additional filter is added to block some or all of the light, leading to "black lights" as used in
discotheques or with equipment for forensic
investigations. For therapeutic treatment there is no strict reason for a strong filtering of the light. The heat production of tube-lights is relatively low and their armatures can therefore easily be produced out of synthetic materials. Because of the low heat production the distance between the lamps and the treated face or body can be kept low without becoming uncomfortable, making UV tube-lights very well suited for face-tanners and sun-lamps.
The ballasting equipment necessary to limit and stabilise the current through a mercury vapour discharge lamp leads to relatively heavy and expensive armatures. This disadvantage can be avoided by using a so-called blended lamp that combines a mercury vapour discharge lamp and an incandescent lamp into a single construction. In a blended lamp a
gas discharge tube is mounted inside the glass- or quartz bulb of the incandescent lamp and it is connected in series with the filament of the incandescent lamp. The filament in fact plays a double role as as well infrared source as serial ballast for the discharge lamp, thus avoiding the use of a heavy and expensive
coil or transformer. The first blended lamps (type 1) consisted of one glass bulb that contained both a drop of mercury and a specially designed filament with a twofold function. The heat of the filament made the mercury to vaporise and at a sufficient high gas pressure a voltaic arc developed that short-circuited a part of the filament. This short-circuited
part than played no further role in the generation of the desired radiation. The part of the filament that stayed in series with the voltaic arc however, now lit up fiercely and served both as a current
limiter and an infrared source. With later designs (type 2) a complete and separately sealed gas discharge tube was mounted within the outer bulb, still in series with the filament that again served as a current limiter and an infrared source. Due to its construction a blended lamp not only emits ultraviolet radiation but also light and infrared radiation and it
certain chemicals might be added to the glass. With the Ultra-Vitalux blended lamps made by Osram for example these additions could be noticed through the typical greyish-pink colour of the glass. Since blended lamps, just like conventional mercury vapour discharge lamps, operate at working temperatures above that of incandescent lamps the
does so in a proportion that very much resembles that of natural sunlight. Thanks to this characteristic blended lamps are applicable for both ultraviolet- and light therapies. In order to reduce the radiation of undesirable quantities of the short waved UV-C,
construction of the armatures they are fitted in is often open and made out of steel.
coefficient the current
ultraviolet radiator only depends on the
In many configurations the infrared radiator may still be used independently however (see electrical circuits).
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appearances and combinations
More often than with infrared radiators, ultraviolet radiators were placed on a standard. For older types of sun-lamps one of the reasons was be the required electrical ballast element for the lamp that, when placed in the base of the armature, allowed for a stable mounting on a standard. For later sun-lamps, like sun canopies for instance, the need to treat larger parts of the body obliged the use of sun-lamps mounted on a standard. Face-tanners and smaller sun-lamps mostly came in a tabletop configuration. The sun-lamp configuration with an infrared radiator that also served as a ballast
for the ultraviolet radiator was partly driven by economic considerations in which the quality of the infrared radiation was less important. Other examples of economic use of resources were the armatures that came with a set of interchangeable elements. Common elements were dull radiators, metal wired elements, quartz elements, infrared- and
coloured incandescent lamps, blended lamps and even discharge lamps. Due to the need for a serial ballast these interchangeable discharge lamps could not be placed into a standard armature directly so they were combined with for instance a quartz tubular into a new unit that as a whole fitted into the socket of the armature.
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 micro-waves. Ultraviolet lasers are also known as excimer- or exciplex lasers, referring to the internal process that takes place in the medium of an ultraviolet laser. In medical science ultraviolet lasers are commonly used in eye surgery.
in 1918, was an incandescent lamp with a spectral