Spectral radiance

Spectral radiance measures radiant power per unit projected area, solid angle, and frequency or wavelength interval. It describes how much radiation travels in a particular direction at each part of a spectrum.

Radiant flux: Radiant flux is the rate at which radiant energy is transferred, measured in watts. Spectral radiance distributes this total power across area, direction, and spectral interval.
Radiative transfer equation: The radiative transfer equation describes how radiation intensity changes along a path through emitting, absorbing, or scattering material. It tracks spectral radiance as sources and interactions alter a beam.
Planck's law: Planck's law gives the spectral radiance emitted by a blackbody at a specified temperature. It predicts thermal spectral radiance from temperature and frequency or wavelength.
Irradiance: Irradiance is radiant power incident on a surface per unit area. It integrates over incoming directions, whereas radiance preserves directional information.
Radiance: Radiance is radiant power per unit projected area per unit solid angle. Spectral radiance adds a frequency or wavelength dimension to this broader quantity.
Specific intensity: Specific intensity is the radiative-transfer quantity of energy carried per area, time, solid angle, and frequency interval. It is the common radiative-transfer name for spectral radiance.
Blackbody radiation: Blackbody radiation is the electromagnetic radiation emitted by an ideal absorber in thermal equilibrium. Its spectrum provides the reference against which real thermal radiance is compared.
Exitance: Radiant exitance is radiant power leaving a surface per unit area. It sums emission across directions instead of resolving each direction.
Solid angle: A solid angle measures the apparent size of an object from a point in three-dimensional space. It specifies the directional spread of the radiation being measured.
Absorption coefficient: An absorption coefficient measures the rate at which a material removes radiation from a beam per unit path length. Absorption reduces spectral radiance along a path through a medium.

Linked from 11 pages