system
Given the following post, respond as if you're commenting on Reddit:
human
Will opening a door darken a room?

Suppose you are trying to sleep in a small room with several doors and a lamp.  It is hard to fall asleep because of the brightness of the lamp.  Will opening the doors "darken" the room (the rooms on the other side of the doors are dark)?  Will some of the photons now travel to the other room as opposed to bouncing off the walls in your room?
gpt
Yes, very slightly. Light that would have previously been reflected off the surface of the door will now move through to the adjacent dark room, lightening it by a very slight degree.

However, the brightness of the lamp itself (as the source of the light) will not get any darker and it won't help you sleep better. This is because you could say that there are two different light sources: the light coming directly from the lamp and hitting your eyes, and the light that is heading out in different directions - away from your eyes - and reflecting off the surrounding walls and doors back at your eyes. The latter is the background light which illuminates the room, while the former is the direct light which is the cause of the glare.

By opening the door, the light is lowered in two subtly different ways: the light that would have reflected off the door and at your eyes is no longer there, and the light that would have reflected off in other directions and scattered / bounced around the room - raising the lux levels around the room in general - is also gone. However, these are both very slight reductions (also mediated by the fact that any light going into the next room could also reflect back, such as if the lamp illuminated the carpet in the open doorway). So, to answer your question, opening a door will probably darken the room *very* slightly, but not the perceived brightness of the lamp itself. Maybe it's time for a dimmer switch?

*/edited for clarity*

/architect with many years of dealing with environmental consultants and lighting engineers.