dome light fade

so i'm admiring my friend's car dome light the other day because it fades off when he closes his door. it was a computer-controlled fade, but i got to thinking, why couldn't a capacitor do the trick? so i tried it out, but quickly realized i need a much bigger capacitor than is practical. so anyone have any tips? is there a way i could do this with relays/capacitors/resistors? or should i stick to icu's controlling it? i also thought i could replace the 8W dome light in my car with an LED and just using a capacitor, but that is less desirable as it's much dimmer. i would appreciate any thoughts/tips anyone has.