# configuration factor, c1→2

[9.5.7.4] The ratio of illuminance on a surface at point 1 that is due to the flux directly received from lambertian surface 2 to the exitance of surface 2. It is used in flux transfer theory.

$C_{1\rightarrow 2}= E_{1}/M_{2}$

Also: the ratio of the differential flux directly received by surface 2 and due to element 1 to the total differential flux emitted by differential lambertian surface element 1:

$C_{1\rightarrow 2}= \left ( d\theta _{1\rightarrow 2} \right )/\left ( d\theta _{1} \right )$

Note: In the literature, this term is also called angle factor, illumination factor, point configuration factor, and sky factor.

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