The Prague Sky Model requires an external dataset file (Apache-2.0 licensed). Phase 1 falls back to Preetham radiance with a console warning if no dataset is loaded.
SunSkyLight is a backward-compatible alias
for Preetham; existing scripts continue to
compile unchanged.
The hemisphere preview is a Java 2D approximation, not a raytraced render. Colours are indicative only.
For highest physical accuracy, use Hosek-Wilkie (RGB) or Prague (full spectral) with GPUFlux.