Spectral colours are the colour impression of a hue with a wavelength between 380 and 780 nanometres that is visible to the human eye - they are known as rainbow colours and are created when white light is refracted through a prism.
The wavelengths of the primary colors
Decomposition of white light into its spectral colors
The decomposition of white light into spectral colours
The first person to scientifically document the splitting of light into spectral colours in 1676 was Isaac Newton. He used a prism for this purpose and shone sunlight through it, whereupon the light was broken down into different colours. There are essentially around 300 spectral colours distinguishable by humans; however, the term is often associated only with the rainbow colours red, orange, yellow, green, blue, indigo and violet.
Incidentally, the term ‘rainbow colours’ was not chosen at random. It is closely linked to the phenomenon of light refraction through a prism: the sun provides white light; the raindrops act as prisms, thereby causing the light to be broken down into its spectral colours.
The indivisibility of spectral colours
When white light hits the prism, the spectral colours are produced, but what happens when a spectral colour hits a prism in turn? Does the human eye perceive further colour changes? Spectral colours are pure colours, which means they cannot be broken down into other colours. So if one were to repeat the prism experiment using spectral colours instead of white light, no new colours would be produced.
