You drive into a brightly lit tunnel which is indicated like this. What do you do?

This sign indicates a tunnel ahead. According to German traffic rules, when you enter a tunnel—even a brightly lit one—you must turn on your dipped headlights. This improves your visibility for other drivers and ensures you can be seen clearly inside the tunnel. Driving without lights or with just daytime running lights is not sufficient because tunnels can have changing light conditions that affect visibility. Using dipped headlights is a safety requirement to prevent accidents in tunnel environments.