Light filters are devices that selectively transmit light of different wavelengths, typically planar glass or plastic devices in the optical path, which are dyed or have interference coatings. Light filters are commonly used in photography (where some special effect filters and absorption filters are occasionally used), many optical instruments, and color stage lighting. Filter is a commonly used filter, which is divided into passband filter and cut-off filter according to spectral characteristics; Spectral analysis is divided into absorption filters and interference filters.