When I was about to leave the building I usually stay in university, all the lights along the corridor were turned off. This is because the lights turn on and off automatically. Concretely speaking, when sensors react with movement of something or someone, the lights are set to turn on. And when sensors react with nothing for a while, the lights are set to turn off.
So, before their reacting with me, I was surrounded by the dark. Its atmosphere made me feel unease, despite that I had seldom seen ghosts.
To tell the truth, I saw a ghost from my car in my elementary school days. The ghost was bandaged whole the body. Though I can't eliminate the possibility that the man bandaged whole the body was really walking or I saw illusion, it was a scare experience.