Definition: Monochromatic light contains light with a single wavelength.
Such radiations are available throughout a wide variety of wavelengths. The electromagnetic spectrum refers to this range of wavelengths as a whole. To acquire illumination of a specified wavelength, a monochromator, a type of light filtering, must be used to filter out undesired wavelengths.
Monochromators are often changeable, allowing for the use of different wavelengths at various times for various purposes. Because different compounds absorb or emit differing light wavelengths, this may be used as a diagnostic instrument for chemical characterization.