Definition: | function describing the change with direction of irradiation (θi,ϕi) and direction of view (θr,ϕr) of the radiance of a surface element (xr,yr) in a given direction of view at a given wavelength λ, Lr(θr,ϕr,xr,yr,λ), with respect to the irradiance incident on the medium from the given direction of irradiation at the given wavelength, Ei(θi,ϕi,λ)
ρ(θi,ϕi,θr,ϕr,xr,yr,λ)=dLr(θr,ϕr,xr,yr,λ)dEi(θi,ϕi,λ) Note 1 to entry: The bi-directional reflectance distribution function is expressed in steradian to the power minus one (sr−1). Note 2 to entry: See also "radiance coefficient". Note 3 to entry: This note applies to the French language only.
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