# 17-25-089

bi-directional reflectance distribution function

BRDF

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, , with respect to the irradiance incident on the medium from the given direction of irradiation at the given wavelength, :

Note 1 to entry: The bi-directional reflectance distribution function is expressed in steradian to the power minus one (sr−1).