Under what circumstances are you required to use your headlights?

Using your headlights whenever the windshield wipers are in use is a requirement in Washington State, as it enhances visibility for both the driver and other road users. This law is designed not only to help the driver see better in adverse weather conditions but also to ensure that vehicles are more visible to others. When the windshield wipers are active, it typically indicates that conditions such as rain, snow, or sleet are present, making it crucial to use headlights to improve safety on the road.

The other options do not provide a comprehensive approach to using headlights. While heavy rain and fog are specific conditions where using headlights is important, the law is broader in scope. Simply using headlights during heavy rain or fog does not account for the visibility issues presented by other weather conditions or at certain times of day when natural light is limited. Thus, the requirement to use headlights with windshield wipers ensures consistent safety measures regardless of the specific type of poor visibility.