Mechanisms for generation of electromagnetic radiation are reviewed.
White light contains a mix of all wavelengths in the visible region.
It was Sir Isaac Newton who first in 1666 carried out an experiment that showed visible light to be a continuous sequence of wavelengths that represented the different color the eye can see. The process of separating the constituent colors in white light is known as dispersion . We measure longer wavelength intervals in units ranging from mm to cm. to meters. The microwave region spreads across 0.1 to 100 cm,which, includes all of the interval used by radar systems. These systems generate their own active radiation and direct it towards targets of interest.