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

Total @R05046@, $$P$$, incident from all directions onto a small sphere divided by the cross-sectional area of that sphere. SI unit is $$\text{W m}^{-2}$$.
1. Mathematical definition: $$E_{o} = \frac{\text{d}P}{\text{d}S} = \frac{\text{d}H_{o}}{\text{d}t}$$. If the @R05046@ is constant over the area $$S$$, $$E_{o} = \frac{P}{S}$$. Equivalent definition: $$E_{o} = \int_{4\pi}L\text{d}\varOmega$$, 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.