HDRI=high dynamic range image,they are 96bit panoramic light probes for high end programs.In bryce we fake the effect with a sphere and a panoramic image around the scene. GI=global illumination,it envolves radiosity(light refraction and stuff,ambience,ect) and creates soft shadows and very smooth results.color radiates of one another.In bryce we fake it with a lightdome,and or trueambience,and other methods....thier is no set in stone way,as people here have various set ups,with different results,effects,strengths&weakness'.

I eat babies.