A color filter is a sheet of transparent material that modifies a light beam by selectively absorbing some colors relative to others. It is used to create special effects in photography, signs, traffic lights, and directional signs in cars, ships, and airplanes. Color filters can also be used to help distinguish between items that are only differentiated by color. Most light sources emit a wide range of wavelengths that cover the entire spectrum of visible light.

However, in many cases, it is desirable to produce light that has a restricted wavelength spectrum. This can be easily achieved by using specialized filters that transmit some wavelengths and selectively absorb or reflect unwanted wavelengths. Color filters are generally constructed from transparent pieces of tinted glass, plastic, lacquered gelatin (for example, Wratten filters) that have been treated to selectively transmit the desired wavelengths and restrict others. The two most common types of filters used today are absorption filters and interference filters. Absorption filters absorb unwanted wavelengths while interference filters eliminate selected wavelengths through internal destructive interference and reflection.

In any filter, a small amount of incident light is reflected from the surface, regardless of the construction of the filter, and a small part of the light is also absorbed. However, these artifacts are usually minimal and do not interfere with the main function of the filter.