Q: When do you need to use your full headlights in Washington state?
A: This question was posed by an editor who said he's recently seen more people driving with their parking lights, or side lights, on instead of using their full headlights in the evening hours.
In case it's not clear what that means, most cars usually have a few different headlight settings. Parking lights (on my car and most cars I've ever driven, at least) illuminate the side lights only and are found somewhere between the "off" position and the full "on" position. Apparently, they were used at one time to indicate that a car was parked, which might be useful if you came upon it on the side of the road.
Sgt. James Prouty of the Washington State Patrol said during times of restricted visibility — heavy rain, darkness — state law requires you to drive with your full headlights on and not just those in-between parking lights.
According to state law, your full headlights need to be on "from a half hour after sunset to a half hour before sunrise and at any other time when, due to insufficient light or unfavorable atmospheric conditions, persons and vehicles on the highway are not clearly discernible at a distance of one thousand feet ahead."
While this doesn't specifically spell out that your headlights need to be turned on when it's raining, if visibility is reduced (like it is during most rainy conditions), your headlights should probably be on. This might fall under the "unfavorable atmospheric conditions" part of that law.