Movie sets are very brightly lit, even for scenes that appear dark onscreen. This is because the more light there is, the better the final picture quality is.
Common flashlights are not particularly bright. It would be hard for them to compete with extra-bright movie lights. However, in movies and TV shows the beam of the flashlight is generally visible, and the beam generally illuminates things clearly.
In general, are flashlights in movies modified to increase their light output?