This is a scene to test objects. It is a cycles version of the Thomas Berglund's LightBox for Blender Internal you can download at "http://www.blendswap.com/blends/scenes/lightbox01/". It has for meshlights inside a box. I have created a material node group for these meshlights, so they only emit light through one side. It uses light falloff node to soften shadows if you want.
It includes two scene, one without light falloff (soft = 0) and another with it. Also it contains four example renders, with chrome and glass materials.
It is made with Blender 2.64 testbuild2
EDIT: Made again with Blender 2.67. I think it solves some problems with new node groups.