| Definition: | regularly transmitting device used to modify the absolute flux level (radiant or luminous) or relative spectral distribution, or both, of the radiation passing through it Note 1 to entry: A distinction is made between selective filters and non-selective filters or neutral filters according to whether they do or do not alter the relative spectral distribution, of the radiation. A selective filter that makes a significant change in the chromaticity of the radiation is called a colour filter; one that alters the spectral distribution but, because of metamerism, transmits radiation of nearly the same chromaticity as that of the incident radiation, can be called a grey filter. Note 2 to entry: This entry was numbered 845-04-105 in IEC 60050-845:1987.
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