## fluence rate, $$E_{\unicode{x26ac}}$$

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:
1. 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.
2. 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.
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)