Smoothing light device

The function of this circuit is to smooth the extinguishing of light in a car. The blue part of the scheme represent the existing electrical installation in every car (SW is the door-button turning internal light on when a door is opened). The green part is the circuit you have to add.

Components:
R1 - 39ohm / 1W
D1 - diode 1A/20V
T1 - PNP transistor 20V/5A, for example BD244C
C1 - Capacitor 4700µF/16V (you will have probably to adjust the capacity for your convenience)

The capacity of C1 must be adjusted regarding the power of light and the extinguishing's time length you want to obtain, for example with 4700µF a 10W bulb is extinguishings during about 5s, a 4W bulb during 20s, and a 2W bulb during 30s. The R1 is not necessary, but without it the SW will not have a long life. When the light is off, the circuit isn't consuming any power.