## photon exitance, $$M_{\text{p}}$$

Also contains definition of: specific photon emission
Synonym: photon emittance
https://doi.org/10.1351/goldbook.P04631
Photon flux, number basis, qp, emitted by an element of the surface containing the source point under consideration divided by the area S of that element. SI unit is s-1 m-2.
Notes:
1. Mathematical definition: $$\text{d}q_{p}/\text{d}S$$. If $$q_{\text{p}}$$ is constant over the surface area considered, $$M_{\text{p}} = q_{\text{p}}/S$$.
2. Formerly called photon emittance.
3. This quantity can be expressed on a @C01019@ basis by dividing $$M_{\text{p}}$$ by the @A00543@. In this case the symbol is $$M_{n\text{,p}}$$, the name 'photon @E02264@, amount basis', SI unit is $$\text{mol s}^{-1}\ \text{m}^{-2}$$; common unit is $$\text{einstein s}^{-1}\ \text{m}^{-2}$$.
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 394 (https://doi.org/10.1351/pac200779030293)