in fig1 a rare - gas low - pressure discharge lamp referenced 10 in its totality with a dielectric barrier layer is shown , the emission maximum of the lamp lying in the uv - a range . the lamp comprises a gastight discharge vessel 12 which in this embodiment is tubular in shape and filled with xenon . the discharge vessel 12 is provided with a luminescent layer 14 all over its inner side , which layer comprises at least one luminescent material which emits in the uv - a range ( 320 - 400 nm ). an additional luminescent material emitting in the uv - b range ( 280 - 320 nm ) may be added so as to adjust the uv - b / uv - a ratio . two electrodes 16 , for example al electrodes or so - called ito electrodes ( ito = indium tin oxide = sno 2 : in ), are provided on the outer side of the discharge vessel 12 , said ito electrodes having the advantage that they are transparent . the so - called dbd ( dielectric barrier discharge ) lamp thus constructed has a high power density and a long operational life which may be more than 20 , 000 hours . the plasma emission spectrum of this lamp covers a narrow emission band whose center lies at 172 nm when filled with xenon , only a few lines of low intensity being emitted in the infrared region at approximately 828 nm . the uv emission spectrum of the lamp now advantageously depends on the choice of the uv - a and uv - b phosphors . in addition , such a lamp provides a 100 % power output in the vuv range ( 140 to 190 nm ) within a few milliseconds . since the lamp type is not limited to a given , in particular tubular shape , it is also possible to manufacture lamps with a planar or curved geometry , as is shown in fig2 and 3 . this lamp type accordingly renders it possible to manufacture , for example , suntanning couches with a very homogeneous light distribution . fig2 and 3 are diagrammatic cross - sectional views of a planar dbd lamp 20 ( fig2 ) and a curved dbd lamp 30 ( fig3 ), respectively . the two lamps each have a respective discharge vessel 22 , 32 which is filled with rare gas and is partly coated at its inner side , i . e . in the region of the desired radiation direction , with a phosphor or a phosphor combination 24 , 34 , as desired , for converting the high - energy uv light generated in the discharge vessel during lamp operation into low - energy uv light . strip - shaped electrodes 26 and 36 are provided on the outside of the respective discharge vessels . to increase the efficiency of the lamps , a uv reflector 28 , 38 is provided on each of the two lamps on the side of the discharge vessel opposed to the desired radiation direction . such a uv reflector may be realized in various ways and be optimized to suit the respective application , for example through the provision of a coating on the discharge vessel , or in the form of a separate uv reflection mirror . an example of the manufacture of a single - component dbd lamp with bsp phosphor in standard glass with a transmission t 312 . 6 nm of 35 % for light of a wavelength of 312 . 6 nm will now be given below . a suspension of bsp in butyl acetate with nitrocellulose as a binder is prepared . the suspension is provided on the inner side of a discharge vessel in the form of a lamp tube of standard glass of 1 mm thickness in a flush coating process , which leads to a 35 % transmission of light with a wavelength of 312 . 6 nm for a typical coating weight of the phosphor layer of 2 to 6 mg / cm 2 . the binder is baked out in a heating cycle with top temperatures between 500 and 600 ° c . the glass tube is sealed and filled with xenon . the gas pressure of the xenon should lie between 200 and 300 mbar . al electrodes are provided on the outer side of the lamp through adhesion or dipping . such a lamp can then be operated with a square - wave ac voltage of 6 kv and 25 khz . the emission spectrum of such a lamp is shown in fig4 while fig5 , and 7 show the emission spectrums of a single - component dbd lamp with sbe phosphor in standard glass ( fig5 ), a xenon gas discharge lamp with an sms phosphor ( fig6 ), and a xenon gas discharge lamp on whose discharge vessel a mixture of 40 % lap and 60 % bsp phosphor was provided ( fig7 ). the methods of manufacturing these lamps all correspond to the method described above .
a rare - gas low - pressure discharge lamp for generating ultraviolet light , in particular for cosmetic or therapeutic purposes , has a discharge vessel which is filled with rare gas and is at least partly transparent to uv light and which is at least partly coated with a phosphor which radiates uv light upon excitation by an excitation radiation produced in the discharge vessel so as to utilize a desired spectral range .