Physical sun light This will model sun lighting from NASA measurements, including atmospheric absorption adjustable through the turbidity parameter. The size of the sun can be tweak from its reference size with the relsize (relative size) parameter. To get a correct effect, the Z axis must point above, the Y axis is north and X axis is east. Physical sky light The physical sky creates a lighting setup that simulates the light of the sun and atmosphere, based on the direction of a sun lamp in the scene and a parameter named turbidity which defines the clearness of the sky. Both the sun angle and the sky clearness influence the colour of the light. Additional parameters called aconst, bconst, cconst, dconst, econst allow you to fine tune the color of the sky to simulate various atmospheric conditions.