If you can see the area lit by their headlights, then you are probably close enough to dim your own.
Common courtesy would be at least 500 feet.
300 feet
According to the California Department of Motor Vehicles, the minimum following distance on highways is three car lengths. Anything closer is considered tailgatinging and is both unsafe and against the law. This distance is independent of time of day.
200 Feet
In most states it is 500 Feet. Common sense should prevail.
The minimum following distance behind another vehicle that should be maintained is typically 3-4 seconds. This allows enough time to react in case the vehicle in front suddenly stops or slows down.
You should dim your headlights within 500 feet of the car in front of you. The rule of thumb is, if you can see another car, dim your lights.
When following another vehicle, it's generally recommended to maintain a distance of at least three seconds behind it, which can be translated to about 100 feet at highway speeds. This distance allows for adequate reaction time in case the vehicle in front suddenly stops. Always adjust your following distance based on speed, road conditions, and weather.
Yes, headlights must be on low beam within 500 feet of an approaching vehicle.
never
when you can see their headlights