Many people, both in the field of paranormal research and those who are a bit more skeptical, have serious doubts as to whether ghosts are actually interacting with these flashlights. Skeptics claim that the flashlights are rigged.
Paranormal investigators unscrew the backs (or fronts) of the flashlights to the point where the light is teetering between on and off. Any slight vibration could cause the flashlight’s electrical connection to activate or deactivate. Investigators do this to make it easier for ghosts to use their energy to control the light.
Other explanations suggest that the light turns on and off in response to the heating and cooling of the light reflector as explained in this article.