High pressure UV lamps due to their higher gas pressure with the lamp produced more spectral lines and a continuum due to recombination radiation. Having a spectrum in the wavelength from 254 to 436 nm peaking at 365 nm.
In UV lamps (Mercury Vapour Lamp, Iron Lamp or GAllium Lamp), the mainstream UV lamp is a mercury lamp.
Mercury Vapour Lamp has three primary spectral output of 254, 312 and 365 nm. Mercury Vapour Lamp is most widely used but when there is a heavier ink or coating lay down, a metal halide lamp becomes useful for this purpose due to its higher UV output intensity.
The Metal Halide Lamp has a broader spectrum between 350 and 450 nm wavelength. Metal Halide Lamp is made through the use of carefully measured minute amount of iron iodide and tin iodide as the additive mixture which modify the original spectrum output of the standard mercury vapour lamp.
The Gallium Lamp has a primary output slightly above the 400 nm wavelength. The Gallium lamp has the effect of introducing spectral lines of 403 nm and 420 nm of the electromagnetic spectrum. This is particularly useful with diazo type processes like emulsion coatings.
The Gallium Lamp (also referred to as 'Exposure Lamp') are used for high resolution film exposure and in photo-polymerization processes. Such processes are, for example, the exposure of diazo materials, microfilms, offset plates and screen coatings but also for the exposure of coating films and photo-resistance materials in the production of printed circuit board.
The special quartz material being used by the lamp absorbs UV radiation and prevents the formation of ozone gas.
UVA ranges from 400 nm - 320 nm and is considered short wavelength. This UVA wavelength is suitable to curing of inks and coating since the optical paths to the photo initiators to the strongly pigmented lacquers or thicker anti-corrosion layers get longer. UVA wavelength is able to deep penetrate the inks and coating layer to achieve effective curing
UVB ranges from 320 nm - 290 nm
UVC ranges from 290 nm - 100 nm which is having longer wavelength then UVA wavelength
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