Radiant Flux
Definition: radiant energy per unit time which is emitted, transmitted, reflected or received by an object
Alternative terms: radiant power, optical power
German: Strahlungsleistung
Categories: 
general optics, 
light detection and characterization, 
optical metrology
Units: W
Formula symbol: <$\Phi_\textrm{e}$>
Author: Dr. Rüdiger Paschotta
Cite the article using its DOI: https://doi.org/10.61835/rkw
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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 the 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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2020-05-23
I would like to find the power per unit area reached.
The author's answer:
Look for irradiance or optical intensity. (Radiant intensity is something different.)