Diffusion Factor (of a diffusing surface, by reflection or by transmission)
The ratio of the mean of the values of luminance measured at 20 and 70 degrees to the luminance measured at 5 degrees 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 uniform diffuser, whatever the value of the diffuse reflectance.
Reference: C.I.E. (extract)
Note 2: The full text of the Reference: C.I.E. definition explains the limitations within which this form of definition can be applied.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
Celsius (previously Centigrade)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM