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.
Polega to na tym, że świecimy światło na drzwi. Odbije się ono i wpadnie do pokoju, jakaś część z powrotem na drzwi, a potem znów do aparatu.