Selfemission

Self-emission is the emission of energy by a system that originates from its own internal energy content, rather than from external excitation. It is commonly discussed in radiometry and spectroscopy as radiation produced by a body at nonzero temperature or by a quantum system returning from an excited state.

Thermal emission, or incandescence, occurs when a material is heated. Its spectrum follows Planck’s law and depends on temperature and the material’s emissivity. As temperature increases, total emitted power rises and the peak of the spectrum shifts to shorter wavelengths.

Spontaneous emission is a quantum process in which an excited state decays to a lower energy level and emits a photon. This does not require an external light field, though the surrounding electromagnetic environment can influence the rate of emission.

Luminescent emission can also be viewed as self-emission when luminescent centers emit after an excitation source is removed; the emission is generated from the system’s internal energy rather than ongoing external power.

Measurement and analysis: Self-emitted radiation is quantified through radiometry and spectroscopy. Key quantities include spectral radiance, total radiant power, emissivity, and temperature. Instruments such as radiometers and spectrometers characterize the spectrum and intensity of self-emitted light.

Applications and relevance: Self-emission underpins thermal imaging, incandescent lighting, and astrophysical observations, where the observed light originates from the object itself. Distinguishing self-emission from reflected or stimulated emission is essential in experiments and diagnostics.