Question:

You are driving at night with your high beams switched on. You see a car ahead. When must you turn off your high beams?

A When you are 500 feet from an approaching vehicle or 200 feet behind another vehicle

Explaination

You are legally required to dip your high beams when you come within 500 feet of an oncoming car or within 200 feet behind another car. It is polite to dip your high beams when you can see them shine on another car. [Night Driving, Chapter 7: Adjust to Driving Conditions, Alabama Driver Manual]