The reason that the TAPS Team goes "lights out" during an investigation is because darkness is said to cause a peak in paranormal activity. It's kind of like when people watch a scary movie & then dread walking into a dark house or even turning of all the lights to go to sleep.
Lights out simply helps the investigation. There's more of a chance of catching self-illuminated objects in the dark. Plus, I've noticed that, at a lot of locations, sightings are during the night. This helps them disprove some claims in the night.
It's the belief that ghosts on ly can be seen at night. But if a ghost is a spirit than a spirit would be around no matter what time of day or night it is. so i don't really get why they don't start thier investigations until lights-out.
I would think their reasoning would be that in the dark, they could catch more of the weaker energy manifestations. Of course, some spirits are able to be seen regardless of the lighting in a given location. I also think they go "lights out" to add to the "eerie" feel that they are trying to acheive. You have to remember that no matter how fact based the show might be, it is still television and they have to keep the audience intrigued.
