GroIMP provides different models for sky-light simulation and ambient light
The Sky object in GroIMP represents the sky environment and ambient lighting and can be placed into the scene similarily to primitive objects. In the wireframe view, it is displayed as a sphere whose position does not affect the scene because it represents a sky sphere at infinity.
Visual effects of the Sky object are not visible in wireframe mode, use POV-Ray to get a ray-traced image which makes use of these objects.
A scene node that provides CIE Standard General Sky illumination using the Perez all-weather sky model.
A scene node that models a uniform (isotropic) overcast sky hemisphere as 72 directional light sources arranged in 6 rings × 12 azimuths.
A physically coupled sun + anisotropic Perez sky model represented as 73 directional light sources: 72 sky elements (6 rings × 12 azimuths) with Perez-weighted power densities, plus 1 direct sun source.