In radiation meteorology, accurate filter measurements are of importance, particularly for the determination of the parameters of atmospheric transmission. This paper attempts to review the more important aspects involved in such filter measurements and includes a summary of the authors' previous investigations concerned with the establishment of the constants for the standard-type filters recommended by the World Meteorological Organization. Tables are given to facilitate correcting solar-radiation measurements made with filter specimens exhibiting different characteristics within the same glass type to standard conditions. Also presented are tabular values indicating the genera1 effect on measurements (made with the series of Schott OG1, RG2 and RG8 filters examined here) introduced by variation of 10 μ in the lower cutoff position (a shift which has frequently occurred in samples of the same glass type from different melts) ; the information relates to solar radiation at specified air mass and turbidity.