Most light sources emit a broad range of wavelengths that cover the entire visible light spectrum.
In many instances, however, it is desirable to produce light that has a restricted wavelength spectrum. This can be easily accomplished through the use of specialized filters that transmit some wavelengths and selectively absorb or reflect unwanted wavelengths. The two most common types of filters in use today are absorption filters that absorb unwanted wavelengths and interference filters that remove selected wavelengths by internal destructive interference and reflection. In any filter, a small amount of the incident light is reflected from the surface regardless of the filter construction and a small portion of the light is also absorbed. However, these artifacts are usually very minimal and do interfere with the primary function of the filter.