photon fluence, Hp,o , Fp,o

Amount of photons (quanta of radiation) incident on a small sphere from all directions, divided by the cross-sectional area of that sphere and integrated over time. Photons per surface area ( $quanta m −2$ ). SI unit is $m −2$ .

Notes:

Mathematical definition: $H p , o = F p , o = d N p / d S = ∫ t E p , o ⁢ d t$ with $E p , o$ the photon fluence rate, integrated over the duration of the irradiation, $t$ . If $E p , o$ is constant over the time interval, $H p , o = F p , o = E p , o t$
This quantity can be used on a chemical amount basis by dividing $H p , o$ by the Avogadro constant, the symbol then being $H n , p , o$ , the name 'photon fluence, amount basis', SI unit is $mol m −2$ ; common unit is $einstein m −2$ .

Source:

PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 395