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 \(\pu{J m-2}\).
Notes:
- Equivalent definition: Irradiance, \(E\) integrated over the time of irradiation.
- Mathematical definition: \(H = \rm{d}Q/\rm{d}S = \int _{t} E\, \rm{d}t\). If \(Q\) is constant over the area, \(H = Q/S\). If \(E\) is constant over the time interval, \(H = E\, t\).
- This term refers to a beam not scattered or reflected by the target or its surroundings. For a beam incident from all directions fluence (\(H_{\rm{o}}\), \(F_{\rm{o}}\)) is an equivalent term.