For interior lighting using IDL, the scene should be entirely surrounded by your room although that is not absolutely necessary.  A dungeon scene would be predominantly lit be torches, definitely a situation which will require point lights with inverse square fall-off.  Much like this scene in my gallery:

http://www.renderosity.com/mod/gallery/index.php?image_id=1941805&user_id=343328&np&np

The problem I have found with this lighting scenario is torch light can cast rather strong and deep shadows which can hide much detail.  If the scene is fairly extensive, i.e., a large room with many actors, you will have problems maintaining an even illumination throughout.  You would need to have your characters wear light-colored clothing to be seen clearly.  Consider how many light sources you require and how much/little room will be utilizing to construct your set.

When I get a chance, I will post the location of the IDL script.