ABSTRACT
There are three general types of filter glasses: (1) colorless-optical glasses with different ultraviolet cutoffs, (2) ionically colored by heavy metal or rare earth ions, and (3) colloidically colored. The optical, thermal, and mechanical properties, chemical resistance, and internal quality of these glasses are carefully controlled and are generally similar to those of optical glasses. Manufacturer's catalogs should be consulted for specific transmission curves and transmittance. Several of the colored filter glasses exhibit photoluminescence [see W. H. Turner, Photoluminescence of color filter glasses, Appl. Opt. 12,480 (1973) and tables later in this section]. Glass filters may be classified according to their optical properties-short wavelength cutoff, long wavelength cutoff, bandpass, band blocking, and neutral density. Filter glasses produced by major manufacturers are listed by groups in the following table.
