250 ft
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.
If you can see the oncoming vehicle then he can see you. Dim your lights at that time.
100 yards
100 feet
500 feet if the vehicle is coming to you, 300 feet if you are following it.
When you get 300 feet from the car coming ahead.
in florida you must dim your headlights from the oncoming traffic at 500 feet. and from the rear at 300 feet.
You should dim your headlights when approaching another vehicle at least 500 feet away. This helps to prevent blinding the other driver and ensures safer driving conditions for both parties. If you're behind another vehicle, you should also dim your lights when you're within 300 feet.
at least 2m
according to Florida handsbook, you must dim your bright headlights within 300 feet of the vehicle ahead.
Here in California, by law it's 500 feet (a football field-and-a-half), but be kind and dim your bright lights well before that.
If you can see his headlights, drop your high beams. In some states its the law 300 feet at least.