https://doi.org/10.1351/goldbook.I03254

radiant power, P, of all wavelengths incident from all upward directions on a small element of surface containing the point under consideration divided by the area of the element. 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 357 (https://doi.org/10.1351/pac200779030293)

- Mathematical definition: \(E = \frac{\text{d}P}{\text{d}S}\). If the @R05046@ is constant over the surface area considered, \(E = \frac{P}{S}\).
- Alternative definition: Integral, taken over the hemisphere @VT07496@ from the given point, of the expression \(L\, \text{cos}\,\theta\,\text{d}\varOmega\), where \(L\) is the
*@R05037@*at the given point in the various directions of the incident elementary beams of solid @A00346@ \(\varOmega\) and \(\theta\) is the @A00346@ between any of the beams and the normal to the surface at the given point. \[E = \int_{2\pi}L\, \text{cos}\,\theta\, \text{d}\varOmega\] - This term refers to a beam not scattered or reflected by the target or its surroundings. For a beam incident from all directions,
*@FT07376@*(\(E_{o}\)) is an equivalent term. - \(E = \int_{\lambda}E_{\lambda}\, \text{d}\lambda\) where \(E_{\lambda}\) is the
*@S05817@*at @W06659@ \(\lambda\).

PAC, 2007,