Final answer:
Drivers must use car headlights during low-light conditions or poor visibility, and headlights function by using mirrors to focus the bulb's light into a directional beam. The physics of this can be explored by calculating the maximum distance at which someone can resolve two headlights, given their separation distance and the pupil diameter.
Step-by-step explanation:
Under normal weather conditions, a driver must use headlights during low-light times, typically between sunset and sunrise, or when visibility is reduced such that you cannot see a significant distance ahead of the vehicle. The question is relating to the physics of vision and light. An example of how to consider visibility distance and the functioning of headlights can be found in a physics problem where the maximum distance at which the human eye can resolve two headlights of a car is calculated given that the headlights are 1.3 meters apart and the diameter of the pupil is 0.40 cm. The solution involves understanding optics and the resolution limit of the eye, known as the Rayleigh criterion. Figure 25.47 describes how mirrors within a headlight create a directional beam, focusing light in a specific direction to improve visibility for the driver. This principle applies to the functionality of the headlights on your car, which are designed to trap light from the bulb and cast it forward as a directional beam to illuminate the road.