rate of photon number per time interval
where Np is photon number, transmitted or received, and t is time
Note 1 to entry: Photon flux, Φp, is related to radiant flux, Φe, of monochromatic radiation by
where h is the Planck constant, and ν is the frequency of the corresponding electromagnetic wave.
Note 2 to entry: For a beam of radiation whose spectral distribution is or , the photon flux can be expressed by , where h is Planck's constant and c0 is the speed of light in vacuum.
Note 3 to entry: The corresponding radiometric quantity is "radiant flux". The corresponding photometric quantity is "luminous flux".
Note 4 to entry: The photon flux is expressed in second to the power minus one (s−1).
Note 5 to entry: This entry was numbered 845-01-26 in IEC 60050-845:1987.
Note 6 to entry: This entry was numbered 17-927 in CIE S 017:2011.