When a light beam passes through a glass prism, the different monochromatic radiations are all the more deflected by refraction the shorter their wavelength. In this way, the red rays are less deflected than the purple ones and the primitive beam of white light becomes an electromagnetic spectrum. An example is the scattering of white light from the sun into the colors red, orange, yellow, green, blue and violet.

Radiation-Matter Interaction according to Quantum Mechanics

In 1905 Einstein proposed that light was made up of particles, called photons, with energy $h\nu$. Photons are absorbed or emitted by matter producing transitions between different allowed energy levels.