The idea is that we could shine some light on the door, it's going to bounce, go inside the room, some of that is going to reflect back on the door, and then back to the camera. And we could exploit these multiple bounces of light.
Rebotará, entrará a la habitación, una parte se va a reflejar en la puerta, y desde allí hasta la cámara, de donde podríamos extraer esos múltiples rebotes de luz.