Q_p = h·ν

where h is the Planck constant and ν is the frequency of the corresponding electromagnetic wave

Note 1 to entry: Photon energy can be emitted, transferred or received.

Note 2 to entry: The energy of monochromatic radiation, Q_PF, by a photon flux of photons of frequency ν is equal to the photon number, N_p, times the photon energy (Q_PF = N_p·h·ν).

Note 3 to entry: The corresponding radiometric quantity is "radiant energy". The corresponding photometric quantity is "luminous energy".

Note 4 to entry: The photon energy is expressed in joule (J = W·s).