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The lowest frequency EMFs (below 3000 Hz, or 3 kHz) are called extremely low frequency (ELF) fields. They are mainly generated by AC current devices and power lines and usually have a frequency of 60 Hz (North America) or 50 Hz (elsewhere).
Frequencies in the kHz (thousand hertz) and low MHz (megahertz, million hertz) region are called radio frequency (RF) fields or radiation and are used for radio and TV broadcasting and two-way radio systems. The RF region is – arbitrarily – broken up into a further alphabet of frequencies like EHF, SHF, UHF, VHF, HF, MF, LF and VLF. In addition to radio transmitter equipment, also computer displays radiate RF waves in the kHz region in addition to the ELF fields associated with their AC power supply.
Frequencies in the high MHz and the GHz (gigahertz, billion hertz) region are called microwave (MW) fields or radiation and are used for cell phones, personal communication systems, microwave ovens and radar systems.
Frequencies above microwave and below visible light (1012 – 1014 Hz) are called infrared radiation. This type of EMF is radiant heat emitted from hot objects like ovens.
Visible light is a narrow band of frequencies around 1015 Hz. Visible light is emitted from atoms when electrons in their outer shells change orbits around the nucleus of the atom.
Frequencies in the spectral region above visible light are - according to increasing frequencies - ultraviolet, X-rays, gamma rays and nuclear radiation. These types of radiation are categorized as ionizing radiation, whereas all frequencies below ultraviolet are called non-ionizing radiation.
Fig. 4: Electromagnetic spectrum.
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