Total number of photons calculated as

with

the amount of photons in einsteins and

the
Avogadro constant.
Note:
Mathematical definition:

for monochromatic radiation of frequency

,
with

the
radiant energy.
Source:
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 396