Final answer:
Headlights should be used when visibility is limited, as they increase both visibility and detectability by other drivers. The dimming of lights can occur due to voltage drops caused by resistance in a power source. Physics can determine the maximum distance at which headlights can be resolved by the human eye using the Rayleigh criterion.
Step-by-step explanation:
Headlights must be activated during times of darkness and when visibility is limited, typically defined as when one cannot see another vehicle or object on the road from a distance of at least 500 to 1000 feet. This rule aims to ensure not only that you can see where you're going, but also that other drivers can see you. When the headlight intensity is high, be cautious not to stare directly into the light, as it can temporarily blind you. If you experience a dimming of your car's headlights or interior lights, this could be due to a drop in voltage as the battery provides power to start the engine or when a high-power device like a refrigerator motor starts up, which can cause resistance inside the battery itself.
Considering the resolution of the human eye, to calculate or determine the greatest possible distance at which a car's headlights (1.30 m apart) can be resolved, one would apply the Rayleigh criterion using the diameter of the pupil (given as 0.40 cm in some scenarios). This physics problem provides insight into the limits of human vision regarding resolving two closely spaced points of light, such as car headlights at night.