Term: radiant intensity, \(I\)
https://doi.org/10.1351/goldbook.R05045

Definition:
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:
0) Mathematical definition: I = dP/dΩ. If the @R05046-2@ is constant over the solid @A00346@ considered, I = P/Ω.
1) Equivalent to I = ∫(λ) Iλ.dλ, where Iλ is the @S05827@ at @W06659@ λ.
2) It is not recommended to abbreviate this term to just intensity because it is confusing.

Related Terms:
1) radiant power (http://doi.org/10.1351/goldbook.R05046-2).
2) angle (http://doi.org/10.1351/goldbook.A00346).
3) spectral radiant intensity (http://doi.org/10.1351/goldbook.S05827).
4) wavelength (http://doi.org/10.1351/goldbook.W06659).
5) radiant power (http://doi.org/10.1351/goldbook.R05046-1).
6) radiant power (http://doi.org/10.1351/goldbook.R05046).

Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 410 (https://doi.org/10.1351/pac200779030293)

Citation: 'radiant intensity, \(I\)' 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

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