Final answer:
By law, headlights must be used from sunset to sunrise, during poor weather conditions with reduced visibility, and when it is difficult to see ahead on the road, with the exact requirements varying depending on local jurisdiction.
Step-by-step explanation:
By law, you are required to use your headlights on your car at certain times for safety and visibility purposes. These regulations can vary by jurisdiction, but commonly, headlights must be used from sunset to sunrise, during any type of inclement weather that causes reduced visibility, and at any time when you cannot see a person or vehicle on the road at a distance of 500 to 1,000 feet ahead. It is essential to know your local laws to understand the specific requirements for using headlights in different conditions.