Corner of the eye is generally considered normal. I often see cats walking around. I have a black cat but I used to have a gray one with stripes, and I often think I see him walking around. But, I know he's not here anymore. But they aren't hallucinations. Sometimes it's just something our mind does. It assigns shapes to things that are not clear. So you see a cat, but it was a light change like you said.

But, my actual hallucinations are never out of the corner of my eye. They are right in front of me. They are of a man in a blue and white striped shirt. My husband used to wear a shirt like that (he hasn't in at leas 5 years.) And he's about the same size and build as my husband. He's there, then gone. Sometimes I see him standing in the dark, it blocks out the light behind him, too, in the window. He's just a shadow figure standing in front of me, then he's gone.

It freaks me out.

But, he has no energy. It's just an image, and then gone. So, I don't think he's a ghost but a hallucination. I don't see him very often. And, in fact, ever since my husband moved his computer into our room, I haven't seen him at all. I ususally see him around our bedroom door.