The radiant flux is a term of radiometry. It is defined as the radiant energy per unit time which is emitted, transmitted, reflected or received by an object. In case of light, it is also simply called the optical power. However, the term radiant flux can be used for any kinds of electromagnetic radiation, including e.g. X-rays, ultraviolet light, infrared light and terahertz radiation.
A related quantity is the spectral flux, defined as the radiant flux per unit frequency or wavelength interval. The units are then W/Hz or W/nm, for example.
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