| quotient of the mean of the values of luminance, L, measured at 20° and 70° (0,35 rad and 1,22 rad) and the luminance measured at 5° (0,09 rad) from the normal, when the surface considered is illuminated normally Note 1 to entry: The diffusion factor is intended to give an indication of the spatial distribution of the diffused flux. It is equal to 1 for every isotropic diffuser, whatever the value of the diffuse reflectance or diffuse transmittance. Note 2 to entry: This way of defining the diffusion factor can be applied only to materials for which the scattering indicatrix does not differ appreciably from that of ordinary opal glasses. Note 3 to entry: For indicating the shape of the scattering indicatrix it is recommended that the diffusion factor, σ, be used for strongly diffusing materials, and the half-value angle, γ, for poorly diffusing materials. Note 4 to entry: The diffusion factor has unit one. Note 5 to entry: This entry was numbered 845-04-89 in IEC 60050-845:1987.
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