Visible light is only one of many forms of electromagnetic energy. Radio waves, heat, ultraviolet rays, and X-rays are other familiar forms. All this energy is inherently similar and radiates in accordance with basic wave theory. As shown in the figure, this theory describes electromagnetic energy as traveling in a harmonic, sinusoidal fashion at the “velocity of light”, c. The distance from one wave peak to the next is the wavelength λ, and the number of peaks passing a fixed point in space per unit time is the wave frequency ν.
From basic physics, waves obey the general equation
c = νλ