reduced luminance coefficient (for a point on a surface) [*r*]

luminance coefficient multiplied by the cube of the cosine of the angle of incidence of the light on the point

Unit: sr^{-1}

NOTE 1 This can be expressed by the equation

*r *= *q* (cos* ε*)^{3}

where

*q* is the luminance coefficient in sr^{-1};

*ε* is the angle of incidence in °.

NOTE 2 The angle of observation, *α*, affects the value of *r*. By convention this angle is fixed at 1° for road lighting calculations.

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