ratio of the radiant or luminous flux reflected in the directions delimited by the given cone to that reflected in the same directions by a perfect reflecting diffuser identically irradiated or illuminated
NOTE 1 – For regularly reflecting surfaces that are irradiated or illuminated by a beam of small solid angle, the reflectance factor may be much larger than 1 if the cone includes the mirror image of the source.
NOTE 2 – If the solid angle of the cone approaches 2π sr, the reflectance factor approaches the reflectance for the same conditions of irradiation.
NOTE 3 – If the solid angle of the cone approaches zero, the reflectance factor approaches the radiance or luminance factor for the same conditions of irradiation.
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