The Colour Spectrum of Light
A spectrum indicates the intensity dispersion of electromagnetic rays as a function of wavelength or frequency.
Originally the word spectrum was exclusively used to mean the range of colour created through the dispersion of white light through an aperture in a prism or grating which was diverted in various strengths (refraction) according to its wavelengths. If the light comes from an annealing gas a sequence of split pictures (line spectrum) is produced.
Each of the spectral lines produced has a colour corresponding to its wavelength. Closely adjacent spectral lines form a so-called band spectrum. Sunlight produces a connected coloured band of violet via blue, green, yellow and orange to red (spectral colours). The visible spectrum range is part of the whole electromagnetic spectrum, which extends from the most shortwave cosmic radiation to the most longwave radio waves.
