https://doi.org/10.1351/goldbook.P04631
Photon flux, number basis, \(q_{\rm{p}}\), emitted by an element of the surface containing the source point under consideration divided by the area \(S\) of that element. SI unit is \(\rm{s}^{-1}\ \rm{m}^{-2}\).
Notes:
- Mathematical definition: \(\rm{d}q_{p}/\rm{d}S\). If \(q_{\rm{p}}\) is constant over the surface area considered, \(M_{\rm{p}} = q_{\rm{p}}/S\).
- Formerly called photon emittance.
- This quantity can be expressed on a chemical amount basis by dividing \(M_{\rm{p}}\) by the Avogadro constant. In this case the symbol is \(M_{n\rm{,p}}\), the name 'photon exitance, amount basis', SI unit is \(\pu{mol s-1 m-2}\); common unit is \(\pu{einstein s-1 m-2}\).