Oct 5, 2022


The number of photons, dNp, emitted, transmitted, or received in an element of time, dt, divided by that element of time:

photon flux

Units: s-1

Note 1: The photon flux emitted by a source in the wavelength interval from λ1 to λ2 can be calculated from the spectral radiant flux:

photon flux


h is Planck’s constant

c is the speed of light

Φλ(λ) is the spectral radiant flux, measured in W/nm

Note 2: To convert to moles of photons, divide by Avogadro’s number (NA):

photon flux

 The unit for photon flux, Φp, is mol/s and is usually expressed in micromoles per second (μmol/s).

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