Why do my headlights sometimes appear to be dimmer than normal?

When stopped at a light, you may notice that your headlights dim, but don’t worry – they’re supposed to do this. Your car’s super-efficient computer is simply doing its job. It automatically adjusts output of the electrical charging system, which helps improve fuel economy and minimize vehicle vibration. While the engine is idle, the computer monitors electrical usage and adjusts the electrical charging system accordingly. It charges just enough to keep up with demand.

You may notice a similar occurrence when you use other electrical accessories, as well. Turn on your air conditioner, for example, and your vehicle’s computer will respond to the added electrical load. As this happens, you may again notice a brief dimming of your lights.