= Radiant intensity
{title2=$I=d\Phi/d\Omega$}
{wiki}
<Radiant intensity> describes how a source distributes its <radiant flux> over directions. A small cone of <solid angle> $\Delta\Omega$ carries approximately $I\Delta\Omega$ when $I$ varies little across it; integrating $I$ over all emitting directions recovers the total <radiant flux>. For a source with <isotropy> emitting $4\pi\,\mathrm W$ over a full <sphere>, $I=1\,\mathrm{W\,sr^{-1}}$ and a $0.01\,\mathrm{sr}$ cone carries $0.01\,\mathrm W$. A planar source satisfying <Lambert's cosine law> instead has direction-dependent <radiant intensity>, even though its <radiance> is direction-independent.
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