car light dimmer

Pulse width modulation techniques are required in order to dimm a 12V light bulb without wasting a lot of power. Modulation frequencies may be as low as 100Hz to reduce EMI radiation

There are a lot of analog PWM ICs suitable for doing that. The good old SG3535 and TL494 may be used, ramping its duty cycle with a capacitor charged or discharged through a current source

Another approach may be to do the PWM and control logic in software using a simple low-cost microcontroller. I've succesfully used the PIC12C family from Microchip for several custom automotive applications. Sometimes going PIC saves a lot of development time in comparison with the equivalent analog solution