[11.5.19] In roadway lighting:
At a surface of a medium, in a given direction, under specified conditions of illumination: The quotient of the luminance of the surface element in the given direction by the illuminance on the medium, expressed by:
q = L/E ,
where:
L is the luminance in cd/m2
E is the illuminance in lx
Unit: sr⁻¹
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