Non-ionizing (or non-ionising) radiation refers to any type of
electromagnetic radiation that does not carry enough energy per
quantum to ionize atoms or molecules—that is, to completely
remove an electron from an atom or molecule.1 Instead of
producing charged ions when passing through matter, the
electromagnetic radiation has sufficient energy only for
excitation, the movement of an electron to a higher energy
state. The region at which radiation becomes considered as
"ionizing" is not well defined, since different molecules and
atoms ionize at different energies. The usual definitions have
suggested that radiation with particle or photon energies less
than 10 electronvolts (eV) be considered non-ionizing. Another
suggested threshold is 33 electronvolts, which is the energy
needed to ionize water molecules. The light from the Sun that
reaches the earth is largely composed of non-ionizing radiation,
since the ionizing far-ultraviolet rays have been filtered out
by the gases in the atmosphere, particularly ox