photon number, N p
Total number of photons calculated as N p = n p N A with N p the amount of photons in einsteins and N A the Avogadro constant.
Mathematical definition: N p = Q h ν for monochromatic radiation of frequency ν, with Q the radiant energy.
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 396