photon irradiance, \(E_{\textrm{p}}\)
Number of photons (quanta of radiation, \(N_{\textrm{p}}\)) per time interval (photon flux), \(q_{\textrm{p}}\), 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 \(\textrm{m}^{-2}\textrm{ s}^{-1}\). Equivalent definition: Integral, taken over the hemisphere @VT07496@ from the given point, of the expression \(L_{\textrm{p}}\, cos\theta\, \textrm{d}\Omega\) the @P04639@ at the given point in the various directions of the incident beam of solid @A00346@ \(\Omega\) and \(\Theta\) the @A00346@ between any of these beams and the normal to the surface at the given point.
  1. Mathematical definition: \(E_{\textrm{p}} = \textrm{d}q_{\textrm{p}}/\textrm{d}S\). If the photon flux is constant over the surface considered, \(E_{\textrm{p}} = q_{\textrm{p}}/S\). Equivalent definition: \(E_{\textrm{p}} = \int_{2\pi} L_{\textrm{p}}\, cos\theta\, \textrm{d}\Omega\).
  2. This term refers to a beam not scattered or reflected by the target or its surroundings. For a beam incident from all directions@P04635@ (\(E_{\textrm{p,o}}\)) is an equivalent term.
  3. This quantity can be used on a @C01019@ basis by dividing \(E_{\textrm{p}}\) by the @A00543@, the symbol then being \(E_{\textrm{n,p}}\), the name 'photon irradiance, amount basis', SI unit is \(\textrm{mol m}^{-2}\textrm{ s}^{-1}\); common unit is \(\textrm{einstein m}^{-2}\textrm{ s}^{-1}\).
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 396 [Terms] [Paper]