So anyways...I've decided I want to learn how to use Blender and Radiance, just like you've done. Which leads me to my question--how did you do that, anyway? A quick search for Radiance and Linux reveals quite a number of possible packages and installation methods.
Most likely, whatever method you used will work for me, since Debian is pretty similar to Ubuntu.
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.