where log {\displaystyle \log } is the common logarithm (base 10), L n {\displaystyle L_{n}} is the luminance of each light source numbered n {\displaystyle n} , ω n {\displaystyle \omega _{n}} is the solid angle of the light source seen from the observer and p n {\displaystyle p_{n}} is the Guth position index, which depends on the distance from the line of sight of the viewer.