Electromagnetic Energy Electromagnetic energy refers to all types of energy that moves with the velocity of light in a harmonic wave pattern.   Electromagnetic waves are described in terms of their velocity, wavelength, and frequency.   All electromagnetic waves travel at the same velocity commonly known as the speed of light. This velocity may change as electromagnetic energy propagates through media of different densities.   The electromagnetic spectrum is the range of wavelengths that the energy travels in a vacuum.   All forms of matter radiate a range of electromagnetic energy.   Peak intensity of the energy shifts toward the shorter wavelengths as temperature of the matter being detected increases. Source: http://rst.gsfc.nasa.gov/   The graphic below illustrates the visible light color distribution as a function of wavelength. Source: http://rst.gsfc.nasa.gov/