photon exposure, Hp

https://doi.org/10.1351/goldbook.P04632
Photon irradiance, Ep, integrated over the time of irradiation for a beam incident from all upward directions. SI unit is m-2.
Notes:
  1. Mathematical definition: Hp = ∫(t) Ep.⁢dt. If the @[email protected] is constant over the time interval, Hp = Ep.t.
  2. This term refers to a beam not scattered or reflected by the target or its surroundings. For a beam incident from all directions photon fluence (Hp,o, Fp,o) is an equivalent term.
  3. This quantity can be used on a @[email protected] basis by dividing Hp by the @[email protected], the symbol then being Hn,p, the name 'photon exposure, 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 394 (https://doi.org/10.1351/pac200779030293)