Final answer:
Drivers are required to switch to low-beam headlights within 150 meters of an oncoming vehicle. This regulation is rooted in practical considerations of human eyesight and safety to prevent dazzling other drivers.
Step-by-step explanation:
When lights are required, drivers must use low-beam headlights within 150 meters of an oncoming vehicle. This rule helps to prevent the blinding of other drivers and ensure road safety. In physics, understanding the limitations of human eyesight, such as resolving the headlights of a car, involves the diffraction limit of the eye. The greatest distance at which a car's two headlights, 1.3 meters apart, can be resolved by the human eye with a pupil diameter of 0.4 cm can be calculated using the Rayleigh criterion for the resolution limit dictated by diffraction.
The relevance of this example to driving rules stems from an understanding of how far apart objects, like car headlights, can be distinguished from one another. Although the question provided involves the physical principles behind determining visibility distances, regulations regarding headlight usage are determined by traffic laws rather than optical physics. Nevertheless, optical physics, specifically diffraction and resolution limits, can provide insights into why certain visual safety guidelines, such as headlight usage distances, are put in place.