When you open the door, the NC switch provides ground and the interior lamps come on. The underlying function of the module is to latch for about 25 seconds when you first open the door.
When you close the door, the module keeps the light on.
The light level holds for about 15 seconds, then starts to fade for about 4 seconds, and goes out. The latest version has a fourth (green) lead for optional connection to the ignition - turning the ignition on will switch the module off, if you connect the green lead.