Used for photography with infrared films. lnfrared film is also sensitive to ultraviolet rays and the shorter wavelengths of the visible spectrum so it is necessary to filter out all but the infrared rays.
R72 passes only infrared rays above 720nm; RM90 passes only that above 900nm. Often used in crime detection, medical photography, detection of distribution of vegetation, etc.
In ordinary photography with infrared film or infrared color film, the Y(K2), O(G), R(25A) and other filters can also be used to change the contrast or color effect.