Used for photography with infrared films. lnfrared film is also sensitive to ultraviolet rays & 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) & other filters can also be used to change the contrast or color effect.