I don't have any technical insight, just my own observations. I hope this helps in some way.
I believe I understand what variable you are talking about. Up until 4.0, I used to use the addon called "Moonshine" to permanently remove character ambient.
http://www.wowinterface.com/download...Moonshine.html
When 4.0 hit and I started figuring out what addons were broken, I came to Moonshine and kept toggling it on and off. I went into Ironforge's Tram - specifically at the end of the line where there's not much lighting in a niche - and carefully examined my character. Regardless of whether or not Moonshine was enabled, the ambient glow provided by my wand pretty much had my character appearing like the right side of the screenshot included on Moonshine's description page.
I could only come to the conclusion that the variable was removed, thereby rendering Moonshine useless.
Again, this is just observation. I'm afraid I can't offer any help beyond that. I hope you're able to find out the information that you seek.