Influence of irradiation intensity and spectral distribution of the irradiation of opal glass MS-20 on its degree of reflectance

White reflectance samples from opal glass with mat surface are often used a s standards for spectral reflectance measurements in the visible spectral r ange. In measurement devices, in which the spectral selection takes place o nly after the irradiation of the sample, the reflection properties of the s amples may be changed by the influence of this irradiation, Samples from op al glass MS-20 were exposed to irradiation of different intensity, duration and spectral composition. The change of reflectance was strongest in the s hort wavelength range (measurement at lambda = 400 nm); above all it is cau sed by the UV-parts of the total radiation, whereby the UV-A-part leads to an increase, in case of present UV-B- and UV-C-parts to a decrease ot the r eflectance. After some time a partial regeneration occurs, however the orig inal state will not again be reached.