The Electromagnetic Spectrum
Light as we know it is just one small part of a greater entity known as the Electromagnetic Spectrum. The Electromagnetic Spectrum describes a range of energy in wave form that we more commonly know as radiation. The range encompasses Gamma rays at one end of the spectrum where the wavelengths are short to Radio waves at the other end where wavelengths are long. The wavelength itself is defined as short, long or somewhere in between by measuring from the crest of one wave to the crest of the adjacent wave.
Other wavelengths beyond Gamma Rays and Radio Waves exist within the electromagnetic spectrum and these are displayed in sequence in the diagram.
The part that we are interested in is the section towards the centre called the visible light spectrum. Nestled between the Ultraviolet and Infra red wavelengths which are not visible to the human eye is the visible light spectrum. The wavelengths here encompass all the colours visible to the human eye ranging in wavelength from 400 nanometers, which we perceive as the colour violet to 700 nanometers, which we perceive as red. One nanometer is equal to one thousand millionths of a metre. All wavelengths outside this range are invisible to the naked eye.
So when we talk about colour we are actually discussing electromagnetic radiation wavelengths. Each colour in the visible light spectrum conforms to a wavelength which can be seen in the diagram. Of course no one sits in a romantic restaurant on a moonlit night and whispers to their date “your eyes sparkle with a wavelength of 500 nanometres”. They would say “blue” and the evening might develop, so the common words we use are better for widespread descriptive purposes.
