## radiant intensity, $$I$$

Also contains definition of: intensity
https://doi.org/10.1351/goldbook.R05045
@R05046-1@, $$P$$, at all wavelengths per solid @A00346@, $$\varOmega$$. The @R05046-2@ emitted in a given direction by a source or an element of the source in a small cone containing the given direction divided by the solid @A00346@ of the cone. SI unit is $$\text{W sr}^{-1}$$.
Notes:
1. Mathematical definition: $$I = \text{d}P/\text{d}\varOmega$$. If the @R05046-2@ is constant over the solid @A00346@ considered, $$I = P/\varOmega$$.
2. Equivalent to $$I = \int_{\lambda}I_{\lambda}\, \text{d}\lambda$$, where $$I_{\lambda}$$ is the @S05827@ at @W06659@ $$\lambda$$.
3. It is not recommended to abbreviate this term to just intensity because it is confusing.
Source:
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 410 [Terms] [Paper]