The electromagnetic spectrum is a continuum of all electromagnetic waves arranged according to their wavelength, and frequency. Types of electromagnetic waves that make up the electromagnetic spectrum are radio waves, microwaves, infrared light, visible light, ultraviolet light, X-rays and gamma rays.
The shortest waves are gamma rays, which have wavelengths of 10e-6 microns or less. The longest waves are radio waves, which can have wavelengths of many kilometres. The range of visible electromagnetic waves consists of the narrow section between 390nm (blue) to 700nm (red).
Figure: The electromagnetic spectrum.