Is there a way to make light bounce off of a mirror, and appear all over the walls? Like in this video? https://www.youtube.com/watch?v=pimq2J9nyDE
Looks to me like they have either been put in during post production, or faked using an animated texture on the surrounding geometry.
Maybe make a bunch of planes in the same positions as the walls in your scene, and use an alpha mapped image sequence to mix between an emission and transparent shader on the planes, that way it would look as if the light is being cast of the mirror onto the walls thats how i would try to do it any way