ratio of the mean of the values of luminance measured at 20° and 70° (0.35 and 1.22 rad) to the luminance measured at 5° (0.09 rad) from the normal, when the surface considered is illuminated normally
NOTE 1 – 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 transmittance.
NOTE 2 – This way of defining the diffusion factor can be applied only to materials for which the indicatrix of diffusion does not differ appreciably from that of ordinary opal glasses.
NOTE 3 – See note to 845-04-90.
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