It was about demons that take possession of humans on the verge of death. They are severely allergic to the light. I believe they first escapes from a cave. Story may take place in upstate New York. I think it was the town bully who fell victim first. Soon most of the town is taken over. Its only safe for people in daylight. The possessed board themselves in basements during daylight hours. The survivors hunt them down in the daytime and expose them to light to destroy them. Excellent horror novel. Been looking for it for a very long time. I wish I could remember the title or at least author.