Most automotive vehicles typically have their interior lights fade out 30 seconds or so after the doors are closed.
The way I understand it, closing the door will usually depress a momentary on/off switch, opening the circuit, isolating the lights from the battery.
Even with that main circuit broken, the lights manage to stay lit for a short period of time before dimming and fading out completely.
I always assumed this was attributable to the use of an inline capacitor but have noticed some aftermarket solutions seem slightly more complex than that. (Images below).
What's actually involved or required in these circuits? ie.
What function/purpose do the additional components provide/serve?
Are they necessary?
1. I understand that an increasing amount of newer vehicles are probably providing this functionality via ECU integration. If your answer is about this; it's probably unrelated to the actual question.
2. This question is more concerned with the electronics involved and is not necessarily exclusive to automotive applications, despite the example provided.