Shutters are often used in windows and can be adjusted to control the amount of light entering a room.

Here are some other possibilities:

* Blinds: Similar to shutters, but made of slats instead of solid panels.

* Curtains: Can be drawn open or closed to control light, but don't offer as much precision as shutters or blinds.

* Diaphragm: Found in cameras, this is a circular opening that controls the amount of light entering the lens.

Let me know if you had a specific device in mind!