Term: radiant exposure, \(H\)
https://doi.org/10.1351/goldbook.R05042

Definition:
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:
0) Equivalent definition: Irradiance, E integrated over the time of @I03255@.
1) Mathematical definition: H = dQ/dS = ∫(t) E.dt. If Q is constant over the area, H = Q/S. If E is constant over the time interval, H = E.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 fluence (Ho, Fo) is an equivalent term.

Related Terms:
1) irradiation (http://doi.org/10.1351/goldbook.I03255).
2) radiant energy (http://doi.org/10.1351/goldbook.R05039).

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)

Citation: 'radiant exposure, \(H\)' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.R05042

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