A spectral coordinate is a numerical value that represents the position of a point on the visible spectrum of light. The visible spectrum is the range of wavelengths or frequencies of light that humans can perceive as colours. A spectral colour is a colour that is evoked by monochromatic light, i.e. either a spectral line with a single wavelength or frequency of light in the visible spectrum, or a relatively narrow spectral band (e.g. lasers). The spectral coordinate can be expressed in terms of wavelength, frequency, or chromaticity, which is a two-dimensional representation of colour based on hue and saturation.
