UV light in sunlight and diffuse sky radiation is especially important. It can cause alterations in the surface of materials, which – accelerated by other climate factors, such as temperature and humidity – lead to the typical symptoms of aging. Staggered simulations of natural weathering in devices requires a restriction of the number of climate values or their cyclic alterations. The Global-UV test unit simulates the most important climate factors which are relevant for aging.
In other test procedures, too much attention is paid to the simulation of the entire global radiation and the simulation of other important climate factors is neglected. However, it is also important that temperature conditioning and humidification are controlled in a reproducible manner and that the air is humidified without aerosols. Moreover, any uncontrolled overheating on account of the radiant heat of the lamps has to be prevented. Test procedures according to DIN EN ISO 4892-2 prescribe e. g. the simulation of the overall range of global radiation, the disadvantage of which is that the influencing factors of specimen temperature and humidity or their cyclic alterations can only be controlled very vaguely. In test procedures with fluorescent lamps according to DIN EN ISO 4892-3 only the simulation of the photochemically effective spectral range ≤400 nm (UV-A and UV-B radiation) is prescribed. This means we dispense with radiation heating of the specimens but gain the possibility of climate conditioning the specimens in the entire natural temperature and humidity range in a precise and reproducible manner. Within the UV-Global test unit, radiation is effected with special fluorescent lamps in the wavelength range from 290 nm to 450 nm.