Also contains definitions of: radiant energy fluence rate, spherical irradiance

https://doi.org/10.1351/goldbook.FT07376

Total radiant power, P, incident from __all directions__ onto a small sphere divided by the cross-sectional area of that sphere. SI unit is W m-2.**Notes: **

*Source: *

PAC, 2007,*79*, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 340 (https://doi.org/10.1351/pac200779030293)

- Mathematical definition: \(E_{\text{o}} = \frac{\text{d}P}{\text{d}S} = \frac{\text{d}H_{\text{o}}}{\text{d}t}\). If the @R05046@ is constant over the area \(S\), \(E_{\text{o}} = \frac{P}{S}\). Equivalent definition: \(E_{\text{o}} = \int_{4\pi}L\text{d}\varOmega\), with \(\varOmega\) the solid @A00346@ of each beam passing through the given point on the surface and \(L\) the @R05037@ of the beam at that point.
- Fluence rate is identical to spherical irradiance and reduces to @I03254@, \(E\), for a parallel and perpendicularly incident beam
__not scattered or reflected__by the target or its surroundings.

PAC, 2007,