The trick to using Blender in tandem with Radiance is to have the right Python script, Brad: this translates your blender scene file into the Radiance format and provides a useful GUI to configure render settings. I don't have a link so
google key words: brad by Fransceco Anselmo.
The latest version Radiance binaries are available for Linux on the
official Radiance site: A tar ball of the source code is available there as well if you want to compile. I use the linux binary. Remember to set the $PATH variable accordingly. Remember that all objects in Blender must be MESH objects only and the materials must be Radiance's own. Blender materials will not translate directly except for basic stuff like color and specularity. Brad comes with a basic collection of materials.