One night, raining, crossing a street, I noticed strange thing about one of the stopped cars: In front of that car's headlamps, it rained dashed lines. I assumed that the car used LED for lights, running on AC, all with the same phase. (I couldn't recognize the model of the car.)
But what benefit do the AC headlights give? Most car lights run on battery so you can use it even when the engine is off. What powers AC car lamps when the engine is off?