radiant exposure, \(H\)

https://doi.org/10.1351/goldbook.R05042
radiant energy, Q, incident from all upward directions on a small sphere divided by the cross-sectional area of that sphere. SI unit is J m-2.
Notes:
  1. Equivalent definition: Irradiance, \(E\) integrated over the time of @I03255@.
  2. Mathematical definition: \(H = \text{d}Q/\text{d}S = \int _{t} E\, \text{d}t\). If \(Q\) is constant over the area, \(H = Q/S\). If \(E\) is constant over the time interval, \(H = E\, t\).
  3. This term refers to a beam not scattered or reflected by the target or its surroundings. For a beam incident from all directions fluence (\(H_{\text{o}}\), \(F_{\text{o}}\)) is an equivalent term.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 409 (https://doi.org/10.1351/pac200779030293)