The universe contains a vast (infinite) range of electromagnetic waves commonly referred to as the electromagnetic spectrum. At the low frequency end of the spectrum there are radio waves with wavelengths measured in metres or even kilometres. As the frequency increases and the wavelength decreases (frequency f = c/λ where c = speed of light (3 × 108 m s−1) and λ is the wavelength in metres) the electromagnetic waves are referred to as microwaves, infrared, visible light, ultraviolet, X-rays, and finally Gamma rays. At the high frequency end of the spectrum Gamma rays have a wavelength λ of the order 1 × 10−12 m. Visible light is only a very small range of the electromagnetic spectrum with wavelength from about 400 to 700 × 10−9 m.
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(2009). Electromagnetic Spectrum. In: Li, S.Z., Jain, A. (eds) Encyclopedia of Biometrics. Springer, Boston, MA. https://doi.org/10.1007/978-0-387-73003-5_504
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DOI: https://doi.org/10.1007/978-0-387-73003-5_504
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