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

Your answer is correct because German traffic rules require you to switch on your dipped headlights when entering a tunnel, even if it is brightly lit. This is to ensure better visibility for yourself and other drivers, improve safety, and make your vehicle more noticeable. Driving without any lights or only with daytime running lights is not sufficient in tunnels, as dipped headlights provide the right level of illumination and beam direction needed in enclosed or semi-enclosed spaces like tunnels. This rule helps prevent accidents caused by sudden changes in lighting conditions when entering the tunnel.