It seems counter-intuitive to turn the lights out on a ghost hunt. After all, the residents experience the ghosts probably 75% of the time when the lights are on.
Here’s some of the reasons for this practice:
Powering down: Hitting the breakers is important to not confuse instruments such as EMF meters with anomalous readings. It also means less chance of air-conditioning/heaters causing drafts and hot spots, electronics going off, and other mechanized items like ice-makers in fridges confusing the hunters.
No light: We’re certainly not people with nightvision ourselves, but using cameras that can read infrared (nightvision) can help to bring out details in a spectrum of vision we don’t possess. It’s believed that in the infrared spectrum we might find something that has trouble showing itself in the human eye’s range.
No interference: Without lots of cars on the road outside, children screaming in yards, telephones ringing, this is an ideal time to do a study. If you don’t want to get confusing sounds and activity in your evidence files that can be explained by human intervention, then nighttime is your time.
Vision: Admittedly, it’s very easy to be distracted by wall hangings, doo-dads on bookshelves, light coming in from a window, et cetera. With the lack of visual spectrum, like a blind person, hunters become keener with their other senses like smell, hearing, and bodily sensations of being touched and becoming cold.
Quiet time: Some hunters believe that nighttime is the witching time (when things of a paranormal nature come out and play). This is a time when homes and businesses are quiet, when if something of a spiritual nature lingered, it could have the place to itself.
I admit, I’ve done ghost hunting in just about every condition. In the daytime, I hear the fans turn on, a plane overhead, a dog barking, and am distracted by the objects in the room and other visual stimulation. I don’t believe phenomenon only happens at night (about half of what I witnessed as a kid was in the daytime), but I do know that when I was resting in bed at night, I knew the sounds of the house and the feels of it, the smells and the sights in the dark. When anything changed, it was immediately apparent. I think it’s telling that I get little evidence in daylight hours, but most of it in the night. Some might ask, “well, why aren’t ghosts out in the daytime?” They are. The problem is, we’re distracted by life and our senses are filled with too much stimulation to discern phenomenon when it’s occurring. You wonder if that’s true, notice next time you go to bed, how many weird shadows you see, strange sounds you hear, how many aches and pains you feel in your body that you didn’t notice at all in the daylight hours.
Hope this explains it for you. I get this question a lot and it’s very complex to answer. Suffice to say, it’s not for mood or ambiance. There’s an actual reason behind what we do.