Designing a dimmer for 12 V is tricky business. The dimmers you find in your home are designed to operate from an AC voltage and use this AC voltage as a fundamental characteristic for their operation. Because we now have to start with 12 V DC, we have to generate the AC voltage ourselves. We also have to keep in mind that we’re dealing with battery-powered equipment and have to be frugal with energy. The circuit that we finally arrived at can easily drive 6 lamps of 10 W each. Fewer are also possible, of course.