Normal, white light is actually made up of a rainbow of different colors, from red and orange to blue and purple. There are many other "colors" of light that we cannot see. These include ultraviolet (UV) and infrared (IR) "light" that is just beyond the range of human vision. They also include more exotic forms of radiation such as X-rays, gamma rays, and radio waves. Together, all of these different "colors" of light are called the electromagnetic spectrum, or EM spectrum for short.

Each section of the electromagnetic (EM) spectrum has characteristic energy levels, wavelengths, and frequencies associated with its photons. Gamma rays have the highest energies, the shortest wavelengths, and the highest frequencies. Radio waves, on the other hand, have the lowest energies, longest wavelengths, and lowest frequencies of any type of EM radiation. In order from highest to lowest energy, the sections of the EM spectrum are named: gamma rays, X-rays, ultraviolet radiation, visible light, infrared radiation, and radio waves. Microwaves (like the ones used in microwave ovens) are a subsection of the radio wave segment of the EM spectrum.