Probably a dumb question that I used to know the answer to, but I'm drawing a blank ATM-

I have a 2d panel background that needs portions backlit when panel lights are turned ON. I know how to do it with a gauge but I've never had a need to backlight the entire 2d panel before. Can I treat the panel background as I do the fuselage bmp's and make a background_L.bmp with an alpha to illuminate portions of the panel ? I couldn't find the info in the SDK's unless I overlooked something. I don't know how the night texture entry in the panel.cfg works, is that what I should be looking into ?