on the lucerne, if we are moving, it usually takes 2 windows to be switched at once to dip the power, but still can happen. On the 07 impala i drove, something about its electrical made it dim the lights with as little as running one window that was not already at its stopping point. I cannot see my truck ever having this type of problem without alternator failure (when i finally get power windows) because i can run my stereo crazy loud, and the only time it will affect anything is when its loud and the truck is off, in which case it will dim the LED lights wired to its stand or the interior lights if they are on.

Other than that, I find it to be much more common on 07+ gm vehicles for the elec. system to be set up in such a way that power windows will dim the lights.