The art book shows a several concept art drawings of a creature called the Light Woman, as well as of a creature called the Light Man. The Light Woman is on page 089, and contains no write up. The drawings are interesting, but all basically consist of different variations of a morbid woman with a circular light for a head (reminiscent of the search light from the lighthouse you can see in game).
A few pages later we have a page devoted to the Light Man, who we can see has a very similar light apparatus attached to its head. The backside of the light actually looks like the way the reverse bear trap does in Saw. Anyways, there's pictures of him in get ups very similar to the first underwater scuba suits, as well as some where there's a lot of chains dragging behind him. A similar picture on another page shows that the chains have hooks attached to them. Another shot depicts him in a wheelchair, with long limbs. All of this can be seen on page 097.
The writeup is as follows:
We were brainstorming an enemy called Light Man, similar to the Keeper. This type of enemy was to be linked with the lighthouse of the hospital, but that idea was never used. – Ikumi Nakamura
If someone could upload scans, that would be awesome.