"Headlights are on for safety." Ever see that statement on the back of a big rig? Headlights improve the visibility that other drivers have of your car. That is one reason California adopted a Vehicle Code section(24400) that requires you to drive with lights on when driving in the rain. The section also includes driving conditions that require you to have your windshield wipers on continuously, such as rain, fog, mist, snow or other atmospheric moisture. So, if you are using your windshield wipers, use your headlights as well!