Section

Irradiation is a mode of transmission of heat that occurs through electromagnetic waves and involves the part of the electromagnetic spectrum that relates to infrared rays corresponding to a wavelength that extends from 1 μm to 100 μm. Any body that has a temperature above absolute zero emits electromagnetic waves due to the perpetual agitation of its molecules. The greater the agitation, the greater the temperature of the body. The energy that a body emits every second in the form of electromagnetic waves depends on its temperature T and on the area S of its surface. This is expressed quantitatively by an experimental law called Stefan-Boltzmann's law:

ΔEΔt = εzST 

the constant of Stefan-Boltzmann (z) has a value equal to 5,64x10-8 J/(sm^2 K^4 ) J

The coefficient ε, called emissivity, is a number between 0 and 1, and depends on the characteristics of the

body’s surface. If the body is black we have ε = 1. The speed with which an object emits energy is directly

proportional to T4 and, therefore, increases very rapidly as the temperature increases.