Radiant flux

Radiant flux is the rate at which radiant energy is emitted, transmitted, reflected, or received, measured in watts. It is also called radiant power.

Radiant energy: Energy carried by electromagnetic radiation, measured in joules. Radiant flux measures how quickly this energy is transferred.
Radiant intensity: Radiant flux emitted per unit solid angle in a specified direction, measured in watts per steradian. It resolves total source flux into its directional distribution.
Luminous flux: A measure of visible light output weighted by the human eye’s sensitivity, expressed in lumens. Unlike radiant flux, it weights optical power by human visual sensitivity.
Photon flux: The number of photons crossing a surface or region per unit time. It counts particles rather than summing their energy as radiant flux does.
Watt: The SI unit of power, equal to one joule per second. Radiant flux is expressed in watts because it is a rate of energy transfer.
Irradiance: Radiant flux incident on a surface per unit area, measured in watts per square metre. It describes received flux after specifying the area of the receiving surface.
Radiometry: The science of measuring electromagnetic radiation, including its power and distribution. Radiant flux is a foundational quantity in radiometric measurement.
Spectral flux: Radiant flux distributed by wavelength or frequency, expressed per unit interval. It separates total flux into its spectral components.
Electromagnetic radiation: Energy propagated through space or matter by oscillating electric and magnetic fields. Radiant energy is carried by electromagnetic radiation across the spectrum.
Radiant exitance: Radiant flux leaving a surface per unit area, measured in watts per square metre. It describes emitted or reflected flux leaving a surface.

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