Colour filter

A colour filter works in the same selective way. A red filter transmits red wavelengths strongly and absorbs most other visible wavelengths. White light passing through it therefore emerges mostly red.

A colour filter is a transparent material whose transmission depends on wavelength. It transmits a selected range of visible wavelengths and absorbs other wavelengths. A red filter, for example, transmits red light while absorbing the other colours in white light, so the emerging light is red.