= Electromagnetic spectrum
The <electromagnetic spectrum> organizes <electromagnetic radiation> by <frequency> or <wavelength>. In vacuum, $c=\lambda\nu$ and the <photon energy> is $E=h\nu$. <Radio waves>, microwaves, infrared, visible light, ultraviolet, X-rays and <gamma rays> belong to the same physical field, with conventional band boundaries.
Different bands couple differently to matter and require different sources and detectors. The visible band is only a small portion of the full range. <Frequency> remains unchanged at a stationary interface, while <wavelength> generally changes with propagation speed, so a quoted <wavelength> needs a medium convention when that distinction matters.
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