Thermal radiation

Thermal radiation is electromagnetic radiation emitted by matter because of its temperature. Its spectrum and intensity depend on the matter’s thermal state and, for real materials, their emissivity.

Black-body radiation: Electromagnetic radiation from an ideal absorber and emitter whose spectrum depends only on its temperature. It provides the reference spectrum used to describe thermal emission.
Electromagnetic radiation: Energy propagated through space by coupled electric and magnetic fields. Thermal radiation is the temperature-driven form of this broader phenomenon.
Infrared thermography: A technique that maps surface temperatures by measuring emitted infrared radiation. It converts thermal emission from surfaces into temperature images.
Ultraviolet catastrophe: The classical prediction that a black body emits infinite energy at short wavelengths. The failure exposed a central problem in classical accounts of thermal emission.
Reflection: The return of a wave from a surface into the medium from which it came. Reflected radiation comes from external illumination rather than the surface's own thermal state.
Planck's law: A formula giving the spectral radiance of black-body radiation as a function of frequency and temperature. It specifies how thermal radiation is distributed across frequencies.
Thermodynamic temperature: A measure of temperature defined by thermodynamic principles and expressed on an absolute scale. Absolute temperature determines the characteristic spectrum and power of thermal emission.
Thermal imaging camera: An imaging device that detects infrared radiation to map temperature patterns. Its detectors record the radiation used in thermographic measurements.
Max Planck: A German physicist whose 1900 theory of black-body radiation introduced energy quantization. His work produced the law that correctly describes the black-body spectrum.
Fluorescence: Light emission following absorption of radiation, typically ending soon after excitation stops. Fluorescence is driven by prior excitation, not solely by temperature.

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