Artificial sources of UV-A
Harmful to eyes can bear not only solar radiation but artificial sources of UV-A. it is Theoretically suitable light source emits a certain amount of UV-A. In everyday life you have to deal with incandescent lamps, gas discharge lamps, of which the most common fluorescent lamps, sometimes with lasers.
The main artificial sources of UV-A are mercury lamps of high and medium pressure, xenon arc lamps, and lamp containing a mixture of various gases, including xenon and/or mercury vapor. More than 90% of the light emitted by the mercury discharge lamp of the low pressure, represented by a wavelength 253-257 nm. If you increase the pressure in the spectrum of mercury lamps have waves of greater length. So, mercury lamps medium pressure, typically used for street lighting, emit UV-A with a length of 365 nm, but the glass of the bulb absorbs all radiation with wavelengths shorter than 300 nm.
Release mercury vapour lamps in quartz blocks (quartz transmits waves of short length), usually referred to as photochemical. They are used as sources of UV radiation in photobiological experiments. Quartz mercury lamps medium and high pressure, called hot quartz lamps that emit in the region of 250-400 nm. They are used in dermatology, phototherapy.
Xenon arc lamps high pressure emit wavelengths from 170 nm and more, including ultraviolet, visible and infrared region. The lamp is filled with a mixture of xenon and mercury vapor, which emits more UV rays. A noticeable amount of ultraviolet light also emit arc xenon flash lamp used in photography.
Fluorescent lamps are gas-discharge tubes of low pressure covered inside with phosphor. The phosphor absorbs ultraviolet rays and emits light of longer wavelength belonging to the visible part of the spectrum. Fluorescent lamps for special purposes, covered inside with phosphor that emits in the ultraviolet region, are used as sources of ultraviolet rays. These lamps in housings made of glass, transparent to UV radiation, serve as artificial sources of sunlight, emitting UV-A and UV-B.
Many polymeric materials conduct of the nearest wave UV-A region, but after a few exposures to the deletion of most of them is reduced.