Light actually originates from the accelerated motion of electrons of atom. Atoms emit light in tiny packets of energy called photons. Photons move through space as electromagnetic waves, which are a form of energy with magnetic and electrical components. The electromagnetic waves travels at the same speed of light (c) through vacuum, no matter what their frequency the number of oscillations per second of a wave is called its frequency, f, and is measured in Hz. The distance between two consecutive maxima is called the wave length denoted by (lamda)
The classification of electromagnetic waves according to frequency is the tlectromagnetic spectrum. Light that we is only one part of this whole spectrum. The electromagnetic spectrum is a contiuous range of waves extending from radio waves to gama rays. The description names of the sections are merely a historical classification, for all waves are the same in nature,differing principally in frequency and wavelength; all travel at the same speed. The underlying principle that makes light and all other electromagnetic waves travel at one fixed speed is the conservation of energy.