The realism of the images is stunning, rivaling that of a photograph. Radiance is actually a suite of programs that work in concert. In addition to the simple primitive shapes, users have access to generator programs that create extrusions, parametrically defined surfaces and objects of rotation. They can take advantage of both procedural and data-driven texture and bump mapping. The unique aspect of Radiance is the wide range of lighting options.
Users specify materials, which define the way light interacts with a surface.
Some materials are self-luminous and simulate a variety of lighting distributions. Others are reflective and behave like plastic, metal and glass with various surface properties. The material BRTDfunc allows for maximum flexibility over surface reflectance and transmittance, providing for spectrally dependent specular rays and reflectance and transmittance distribution functions. Radiance is Unix-based and the source code and documentation are available for download at the Radiance web site . While you're visiting there, it's well worth your time to take a look at the Image Gallery.