Let's see... The guy in the basement I couldn't see with my eyes, only with my "mind's eye." Hard to explain. If I averted my eyes from the spot I could see him plain as day in my mind. He was about six foot three or four, burly, with black hair and a black beard, a red flannel plaid shirt, khaki-colored pants, and workboots. He had dark eyes, too. Sometimes he had a grin on his face. There was a heaviness in the air wherever he stood. I talked to him a few times but it made my hair stand on end when he responded (not out loud, just like words standing in my mind) so I didn't do that too often. Besides, I didn't want to encourage contact because he seemed to like me a little too much.
The first time I saw him I told myself there was no way a big man like that could fit through a little teeny basement window, so he couldn't be there. They seem real like that sometimes. The first time we tried to smudge him away, he seemed really puzzled and just stood there looking at us like he couldn't figure out what we wanted. He got really quiet for a few days, then started showing up in other parts of the house.
No luminescense. It was more like a snapshot, like there was really somebody there.
As for the guy in the museum, he was standing on a landing inside a historic house when my husband and I came into the room. He was just standing there looking at his hat that he had in his hands. Then he put it on his head and followed us halfway down the stairway. He was just minding his own business, though, didn't seem to notice us. He was so vivid I thought he was a fellow visitor to the exhibit. Seemed real.
Usually it's more like seeing something out of the corner of your eye. If you look straight on you can't see anyone. Also, there's sort of a projected presence that emanates from them that isn't there with a living person. The air around them is slightly charged. I'm not describing it well, but I've never articulated it before.
Thank goodness they never look like the ghouls in Sixth Sense or I'd be cowering under the covers every night.