In light absorption, a distinction is made between basic absorption and absorption due to contamination. Up to wavelengths of about 1,600 nm, the basic absorption is decisive for the attenuation and cannot be influenced by the manufacturing process. The situation is different for absorption due to impurities. These must be reduced as far as possible in the quartz glass melt. The absorptions have a direct influence on the usable wavelength ranges, which are expressed in the optical windows.