If you want to completely avoid those edge light leaks, delete the three infinite (exterior) lights and instead use spotlights or area lights inside the model. You might even use mesh lights for fluorescent tubes or sodium vapor bulbs, but that would require engaging indirect diffuse lighting in the Firefly render settings.

Also, I notice that you had diffuse value = 1 and specular value = 1 on the cube material; generally, those should total less than one (conservation of light energy).

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5