An algorithm has been developed for calculating the area of ​​light apertures in buildings with various systems of overhead natural lighting of premises, allowing for a transition to differentiated accounting of light climate resources in any geographical point on the globe. A mathematical model of the room lighting regime has been improved, taking into account the features of redistribution of light fluxes in the structures of point and strip type skylights, rectangular light-aeration lanterns and in inclined lighting devices. Based on calculations of the amount of lighting in the annual cycle (this criterion has a physiological justification and ensures average annual labor productivity) using a mathematical model and its software implementation on a computer, light climate coefficients for the city of Nalchik were obtained. For light apertures located in an inclined plane, the values of these coefficients change depending not only on the orientation of the light apertures to the sides of the horizon, but also on the angle of their inclination. The difference in coefficients can exceed 40%. Using the obtained coefficients when calculating natural lighting of premises will reduce the area of light openings by 8–15% while maintaining a full-fledged light environment and improving the microclimate in the premises, and thereby increase the technical and economic efficiency of overhead natural lighting systems.