system
Given the following post, respond as if you're commenting on Reddit:
human
Why do radiologists always keep it dark in the room where they take x-rays? Does visible light affect the x-ray exposure?
gpt
The region of the patient's body that will be exposed and visualized through x-ray based imaging is commonly shown in the room by a light beam projected from where the x-rays originate.  By keeping the room dark, a radiologist or x-ray tech can see whether the patient is properly positioned with respect to the beam.

The light beam also allows the radiologist to adjust the beam so that it focuses on as small a region as possible without missing the anatomic structures of interest, a process known as "collimation."  Collimating the beam reduces x-ray photon scatter, which in turn improves image sharpness. It also reduces patient exposure.