https://doi.org/10.1351/goldbook.P04636
Number of photons (quanta of radiation, \(N_{\rm{p}}\)) per time interval. SI unit is \(\rm{s}^{-1}\).
Notes:
- Mathematical definition: \(q_{\rm{p}} = \rm{d}N_{\rm{p}}/\rm{d}t\). If the number of photons is constant over the time interval, \(q_{\rm{p}} = N_{\rm{p}}/t\).
- This quantity can be used on a chemical amount basis by dividing the photon flux, number basis, \(q_{\rm{p}}\), by the Avogadro constant, the symbol then being \(q_{n\rm{,p}}\), the name 'photon flux, amount basis', SI unit is \(\pu{mol s-1}\); common unit is \(\rm{einstein s}^{-1}\).
- Although the symbol recommended by CEI is \(\mathit{\Phi} _{\rm{p}}\), the symbol \(q_{\rm{p}}\) is preferred since \(\mathit{\Phi}\) is reserved for quantum yield.