Solarization-resistant glass composition having a UV-cutoff with a definite transmittance gradient and radiating device for a weathering apparatus containing a glass of said composition

The borosilicate glass with improved solarization-resistance has a transmittance curve within an area bounded by respective curves defined by the corresponding equations τ=1.7·(λ−277) and τ=1.6·(λ−284) in a wavelength range of 283 nm to 325 nm. This glass has a composition, in wt. % based on oxide content, of: 55-82, SiO2; 10-20, B2O3; 1-10, Al2O3; 0-5, Li2O; 0-10, Na2O; 0-10, K2O; 0-10, M2O; 0-5, MgO; 0-10, CaO; 0-5, SrO; 0-15, BaO; 0-15, MO; 0-3, ZrO2; 0-5, ZnO; 0-2, CeO2; 0-3, WO3; 0-2, SnO2: 0-0.1, Fe2O3; 0.05-2, MoO3; 0-5, Bi2O3; 0-1, TiO2 and 0-5, oxides of selected rare earth and Group IVB to VIIIB elements. The transmittance is adjusted by varying the MoO3 content and if necessary the TiO2 and Bi2O3 content. The glass is especially suitable for use in a weathering apparatus.