Section: 10 | Classification of Electromagnetic Radiation |

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CLASSIFICATION OF ELECTROMAGNETIC RADIATION

David R. Lide

Through historical usage and, in some cases, action of standardization bodies, the electromagnetic spectrum has been divided into frequency bands or regions where the character of the radiation is similar. Table 1 shows a division into decade frequency steps running from 3 Hz to 30 ZHz (30 × 10²¹ Hz), i.e., from low radio frequencies (RF) to γ-rays. The second column gives the approximate wavelength range corresponding to each frequency range. The wavenumber range and approximate photon energy range are also given. The last column gives the designation of each of the bands. The bands up to 3 THz frequency have been given letter designations by the International Telecommunication Union (ITU), but it should be noted that many other designations are in use. The higher frequency regions are labeled by historical terms like infrared (IR), visible, ultraviolet (UV), etc. There are no sharp boundaries between these regions, and usage varies.
The exact relations between these parameters are:

ν = c/λ = ck
λ = c/ν= 1/k
k = ν/c = 1/λ
c = speed of light = 2.99 792 458 × 10⁸ m/s

The major regions are illustrated graphically in Figure 1.

The microwave region, which is usually considered to extend from about 1 GHz to 300 GHz, has been subdivided into several bands that are given arbitrary letter designations. These bands, which are important in communications and radar technology, are listed in Table 2.

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TABLE 1. Frequency, Wavelength, Wavenumber, and Energy Ranges of Radiation Bands in Decade Steps

Frequency (ν)	Wavelength (λ)	Wavenumber (k)	Approximate photon energy	Band name	Band designation
Continued on next page...
3 Hz – 30 Hz	10⁸ – 10⁷ m	10^-8 – 10^-7 m^-1		Extremely low frequency	ELF (ELF 1)
30 Hz – 300 Hz	10⁷ – 10⁶ m	10^-7 – 10^-6 m^-1		Super low frequency	SLF (ELF 2)
300 Hz – 3 kHz	10⁶ – 10⁵ m	10^-6 – 10^-5 m^-1		Ultralow frequency	ULF (ELF 3)
3 kHz – 30 kHz	100 km – 10 km	10^-5 – 10^-4 m^-1		Very low frequency	VLF
30 kHz – 300 kHz	10 km – 1 km	10^-4 – 10^-3 m^-1		Low frequnecy	LF
300 kHz – 3 MHz	1 km – 100 m	10^-3 – 10^-2 m^-1		Medium frequency	MF
3 MHz – 30 MHz	100 m – 10 m	10^-2 – 10^-1 m^-1		High frequency	HF
30 MHz – 300 MHz	10 m – 1 m	10^-1 – 10⁰ m^-1		Very high frequency	VHF
300 MHz – 3 GHz	1 m – 100 mm	10⁰ – 10¹ m^-1		Ultrahigh frequency	UHF
3 GHz – 30 GHz	100 mm – 10 mm	10¹ – 10² m^-1		Super high frequency	SHF, microwave
30 GHz – 300 GHz	100 mm –10 mm	1 - 10 cm^-1		Extremely high frequency	EHF, microwave
300 GHz – 3 THz	1 mm – 100 µm	10 – 100 cm^-1		Far infrared	THF, far IR
3 THz – 30 THz	100 µm – 10 µm	100 – 1000 cm^-1		Mid infrared	Far IR, mid IR
30 THz – 300 THz	10 µm – 1 µm	1000 – 10,000 cm^-1	0.1 eV – 1 eV	Near infrared	Mid IR, near IR
300 THz – 3 PHz	1 µm – 100 nm	1 – 10 µm^-1	1 eV – 10 eV	Near ultraviolet, visible	Visible, near UV
3 PHz – 30 PHz	100 nm – 10 nm	10 – 100 µm^-1	10 eV – 100 eV	Extreme ultraviolet	Far (vacuum) UV
30 PHz – 300 PHz	10 nm –1 nm	100 µm^-1 – 1 nm^-1	100 eV – 1 keV	Soft x-ray	Soft x-ray
300 PHz – 3 EHz	1 nm – 100 pm	1 – 10 nm^-1	1 keV – 10 keV	Soft x-ray	Soft x-ray
3 EHz – 30 EHz	100 pm – 10 pm	10 – 100 nm^-1	10 keV – 100 keV	Hard x-ray, soft γ-ray	Hard x-ray, soft γ-ray

Abbreviations for radio frequency bands: EHF–extremely high frequency; ELF–extremely low frequency; HF–high frequency; ITU–International Telecommunications Union; LF–low frequency; MF–medium frequency; SHF–super high frequency; SLF–super low frequency; UHF–ultra high frequency; ULF–ultra low frequency; VHF–very high frequency; VLF–very low frequency.

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CLASSIFICATION OF ELECTROMAGNETIC RADIATION

TABLE 1. Frequency, Wavelength, Wavenumber, and Energy Ranges of Radiation Bands in Decade Steps

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