Well if it's actually still under warranty, I'd definitely take it to them. If not , No I don't think it's a problem, with your car idling that low, the alternator just isn't spining fast enough to generate the needed power for what ever your running plus your head lights. This way, when you raise your idle, it will bump up your alternator speed, and you won't notice it any longer, because the amount it goes up wil be negligable.

The same way your idle goes up when your ac goes on, is the same thing thats happening, it just sounds to me like your idle is too low. Have you ever changed it from factory??????

Later,