Automatic Luminance or Photometrics automatically adjusts the overall intensity of your rendering, much like the automatic exposure on a camera.
In this first image I have locked the Luminance, then lowered the lights and turned self glow off in order to get a somewhat dim scene.
Then, leaving Luminance locked I added self glow to the back panels. This gave me the desied effect of increasing the intensity of the panels, and their reflection in the mirror, without compensating by lowering the intensity of other objects.
Enjoy! - But use with care.
Note: Locking only works properly after the first pass has rendered - since the initial value of Average Luminance needs to be calculated while rendering.