Electromagnetic radiation or radiant energy moves through space and air in waves like ocean swells. Electromagnetic waves are classified by their wavelength, which is the distance from one crest to the next. Radio waves have the longest wavelengths, and gamma waves have the shortest wavelengths. Visible light — the only part of this spectrum that we can see — falls in between.

All forms of radiation are basically the same. When any form of radiant energy is absorbed by an object, the molecules in the object move more energetically. As a result, the object's temperature increases correspondingly.

Figure 2 Temperature Temperature is a measure of the motion of atoms, molecules and free electrons. Click on image to toggle between low and high temperatures.