Origin of Radiation

The origin of radiation is almost as old as the history of the creation of matter. The term “radiating energy” is used to refer to energy conveyed by electromagnetic waves. This chapter uses the terms “exchange” or “transfer by radiation” to refer to all of the energy transfers occurring at a distance, between bodies, by electromagnetic waves. It presents the electromagnetic wave spectrum with the wavelengths and corresponding frequencies. This spectrum covers all of the radiations encountered in nature, including cosmic radiations, X-rays, microwaves, telephone waves and radio waves. The range of wavelengths between 0.1 µm and 100 µm admits specific characteristics: when electromagnetic radiation belonging to this range reaches a given surface, it produces excitation of the matter, which is reflected by an increase in the temperature: this is thermal radiation. The chapter also summarizes the characteristics of the different regions of the electromagnetic spectrum.