Final answer:
You must switch to low beams at least 500 feet before meeting oncoming vehicles or when following another vehicle within 300 feet. Check local laws for the exact requirement.
Step-by-step explanation:
When meeting or following a vehicle at night, you must dim your headlights to low beams to prevent blinding the other driver. The distance at which you must switch to low beams is usually mandated by law, and it can vary by jurisdiction. In many places, it's required to switch to low beams at least 500 feet before meeting oncoming vehicles or when following a vehicle at a distance of 300 feet or less. It is important to always refer to your local traffic laws to determine the exact distance required in your area.
The ability to resolve two headlights as separate points of light, or the resolving power of the eye, relates to the subject question by considering safety and visibility at night. The headlights of a car that are 1.3 m apart can be resolved at a distance where the angle of separation between them is greater than the resolution limit of the human eye (Rayleigh criterion).