= Lambertian reflectance
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<Lambertian reflectance> is the ideal diffuse-reflection model with direction-independent outgoing <radiance>, the <frequency>-integrated <specific intensity>. If a fraction $0\leq\rho\leq1$ of incident <radiant flux> is reflected, a surface receiving <irradiance> $E$ has reflected <radiance> $L=\rho E/\pi$. The reflected outward <power> per <area> is $\pi L=\rho E$ by the same hemispherical integral used for <radiant exitance>. Its <radiant intensity> still acquires the <projected area> factor in <Lambert's cosine law>.
For $E=100\,\mathrm{W\,m^{-2}}$ and $\rho=0.80$, the reflected <radiance> is $80/\pi\approx25.4648\,\mathrm{W\,m^{-2}\,sr^{-1}}$. A patch of <area> $0.020\,\mathrm{m^2}$ reflects $1.6\,\mathrm W$ in total, and its <radiant intensities> at $0^\circ$ and $60^\circ$ are respectively $1.6/\pi$ and $0.8/\pi\,\mathrm{W\,sr^{-1}}$. The <radiance> stays fixed as the view changes, provided the illumination stays fixed. Changing the incident <angle> can change <irradiance> and therefore the reflected <radiance>.
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