Electromagnetic
Spectrum










The electromagnetic spectrum is the range of electromagnetic radiation, as measured by their frequencies and wavelengths. The full spectrum extends from a frequency of zero Hertz (infinite wavelength) to infinite Hertz (zero wavelength), though some scientific theories place upper and lower boundaries on the wavelengths as (a) the size of the universe for the upper limit and (b) the Planck length(1) for the lower. Only a limited portion of the full spectrum is of interest to us; mostly those frequencies in the radio/microwave bands.

The International Telecommunications Union (ITU) has subdivided the radio/microwave region of the spectrum into nine frequency bands, as shown below. The designations include a Band Number and a two- or three-letter Abbreviation. By convention, spectrum charts that include frequencies above and/or below the radio/microwave region follow the frequency division pattern and usually provide abbreviations. No band numbers are included, as they are ITU-specific.

Below are three tables listing the spectrum bands in order of increasing frequency. The tables include those bands a) below the radio/microwave bands; b) the radio/microwave bands; and c) those above the radio/microwave bands.

Bands Below the Radio/Microwave
 
Symbol
Frequency
Range
Wavelength
Range
 
Description
 ELF  3 - 30 Hz
 100,000 - 10,000 km
 Extremely Low Frequency
 SLF  30 - 300 Hz
 10,000 - 1,000 km
 Super Low Frequency
 ULF  300 - 3,000 Hz
 1,000 - 100 km
 Ultra Low Frequency


Radio/Microwave Bands
 
Symbol
 Frequency
Range
Wavelength
Range

 ITU Band No.
 
Description
 VLF  3 to 30 kHz  100 - 10 km
 4  Very Low Frequency
 LF  30 to 300 kHz  10 - 1 km
5
 Low Frequency
 MF  300 to 3,000 kHz  1,000 - 100 m
 6  Medium Frequency
 HF  3 to 30 MHz  100 - 10 m
 7  High Frequency
 VHF  30 to 300 MHz  10 - 1 m
8
 Very High Frequency
 UHF  300 to 3,000 MHz  1,000 - 100 mm
9
 Ultra High Frequency
 SHF  3 to 30 GHz  100 - 10 mm
 10  Super High Frequency
 EHF  30 to 300 GHz  10 - 1 mm
11
 Extremely High Frequency
 - -
 300 to 3,000 GHz  1,000 - 100 µm 12
 Infrared


Bands Above the Radio/Microwave
 
Symbol
 Frequency
Range
 Wavelength
Range
 
Description
 IR  3 - 30 THz
 100 - 10 µm  Infrared
 IR  30 - 430 THz
 10 - 1 µm  Infrared(2)
 - -
 430 - 750 THz
 700 - 400 nm
 Visible Light
 UV  750 - 3,000 THz
 1,000 - 100 nm
 Ultraviolet(2)
 UV  3 - 30 PHz
 100 - 10 nm
 Ultraviolet
 X  30 - 300 PHz
 10 - 1 nm
 X-Rays
 X  300 - 3,000 PHz
 1,000 - 100 pm
 X-Rays
 X  3 EHz - 30 EHz
 100 - 10 pm
 X-Rays
 - -
 30 - 300 EHz
 10 - 1 pm
 Gamma Rays
 - -
 300 - 3,000 EHz
 1,000 - 100 fm
 Gamma Rays





Notes:
1. In physics, the Planck length is a unit of length equal to 1.616229(38)×10−35 meters.
2. The infrared and ultraviolet bands do not strictly follow the frequency range divisions of "on the 3s", as they bracket the visible light band.
3. See our Metric Prefixes page for descriptions of the frequency and wavelength unit prefixes.

References:
1. The official table of radio/microwave band designations is in Article 2, Section I of the ITU-R -Radio Regulations. A somewhat expanded version is in ITU Recommendation ITU-R V.431-7, Nomenclature of the Frequency and Wavelength Bands Used in Telecommunications.
2. See this Wikipedia page for more details on the Electromagnetic Spectrum.