In roadway lighting:
r = q(cos γ)3 ,
q is the luminance coefficient in sr-1
γis the angle of incidence in degrees (the road surface is flat and not sloped up-down or right-left)
Note 1: The angle of observation α, affects the value of r. By convention, this angle is fixed at 1° for roadway lighting calculations.
Note 2: The reduced luminance coefficient is used for determining the luminance of a point of infinitesimal size in the roadway luminance formula.
NOTE: This term was added in RP-16-17 Addendum 3.
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