Radiation is the process of transfer of heat from a hot body to a cold body directly without heating the space between the two bodies. This process of heat transfer does not require any medium. The energy so radiated is called radiated energy. The sun gives light and also heat. Heat transferred by the sun is via radiation. During cold winter nights people gather around a fire to keep warm. This heat is transferred by radiation.
Properties of thermal radiation
Thermal radiation once radiated behaves like an electromagnetic wave.
It also obeys the laws of optics on account of its wavelength being comparatively small to obstacles.
The radiation emitted by a body is a mixture of waves off different wavelengths. However, only a small range of wavelength has significant contribution to the total radiation.
The dominant frequency (or color) range of the emitted radiation shifts to higher frequencies as the temperature of the emitter increases.