Late 90's Fisher Pierce model 7571B. These are probably my favorite set up. Literally built like tanks. I have never found a defective model of this PC and have come across hundreds. (black housing) Very solid and reliable.
The window is seperate, same as the gray ones. Kinda odd. Lol. I don't think we actually used these, I found it in the basement with a bunch of experimental PC's so I asked if I could have it.
Maybe these were demo photocontrols that a sales person would show to customers. Usually with a clear cover, they are upward facing photocontrols. Unless they're those low profile thermal units.
Is the window a separate piece or is it molded into the cover?