${\displaystyle q_{\text{e}}=\frac{L_{\text{e}}}{E_{\text{e}}}}$

where L_e is radiance and E_e is irradiance

Note 1 to entry: The bi-directional reflectance distribution function (BRDF) is similar to the radiance coefficient except that it is defined for directional incident radiation.

Note 2 to entry: The radiance coefficient is expressed in steradian to the power minus one (sr⁻¹).

Note 3 to entry: This entry was numbered 845-04-70 in IEC 60050-845:1987.