radiant exposure, H

https://dx.doi.org/10.1351/goldbook.R05042
Radiant energy, Q, incident from all upward directions on an 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 irradiation.
  2. Mathematical definition: H = d Q / d S = ∫ t E ⁢ 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 o,F o) is an equivalent term.
Source:
PAC, 2007, 79, 293 (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 409