The simplest radiosity lightmaps generation method was described in this article. Screenshots from the program with various position of a light source:

You can download program source code from this page. Program is written on Delphi 6. You will see a window with main menu on the left side:

Select light position with main menu. You can choose position of a lamp: ceil/floor. All lightmaps are filled by black color (only lamp is visible, read opengl radiosity). Click "create lightmaps" or "load lightmap" button.

Program source code: glrnew.zip - 185kb.