I will stab a total guess. But reading from your post, the V-Meter readings don't sound that out of line, considering you had the car under load and then not under load and it didn't go too far out of range.
If your lights are dimming at idle/load ranges that is to be expected when you have accessories running & such. Mine do whenever I have my stuff going.
But again, I'm no expert. I could be totally off. I just think if you're not having problems, with lighting, performance or such a temporary dimming is normal.
