radiant intensity, I

also contains definition of: intensity
https://doi.org/10.1351/goldbook.R05045
Radiant power, P, at all wavelengths per solid angle, Ω. The radiant power 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 angle of the cone. SI unit is W sr−1.
Notes:
  1. Mathematical definition: I=dP/dΩ. If the radiant power is constant over the solid angle considered, I=P/Ω.
  2. Equivalent to I=∫λIλdλ, where Iλ is the spectral radiant intensity at wavelength λ.
  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]
Citation: 'radiant intensity' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.R05045 RIS BibTex EndNote
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