I experienced protracted strobe-like lights from an unidentifiable airial source while traveling West on SR 8 near McCleary, WA between approximately 47.049197, -123.237347 and 47.044459, -123.256487. The event occurred around 11:10pm PST and lasted for approximately 15-20 seconds. I was traveling with my mother. She was driving approximately 65 mph; I was in the backseat resting. After turning a corner and entering a dark stretch of road, we both noticed a prominent white light behaving in a strobe-like manner in the car's interior. We assumed that a State Patrol officer was pulling us over for speeding, even though the light was just white. As the light continued, we noted that no automobiles were visible from any direction and no sources of light were visible from beyond the trees that line SR 8. The light seemed to move about our vehicle's interior while flashing. It was visible in both the front and rear sections of the car. Prior to seeing the light, the car's interior was only illuminated by dashboard controls. After the light stopped, the car's interior illumination returned to baseline. After the light stopped, we slowed the car dramatically to examine our surroundings. We could not detect noise or lights that would commonly be associated with aircraft; we could not discern sources of direct or refracted light from the roadside. Weather was slightly overcast yet fair; the moon was covered by clouds and did not provide significant illumination; we did not experience lightning or adverse weather events. We did not have electronics in the car that could have accidentally emitted light: my mother's cellphone was off and my iPhone lost its charge about 20 minutes prior to the light. The car functioned perfectly throughout the ordeal and its clock matched my watch with no indication of "lost time."After returning home, we roughly approximated our experience by shining a cellphone flashlight on the roof of the car in the dark and oscillating it quickly. We are considering the possibility that something emitted light onto the roof of our car - from above - during the event.