Ship's deck prism

The wide part is embedded in the ship's deck, providing light below through the prism. This is a replica and it belonged to my father. To me, it's a primitive, but beautiful object and reminds me of Dad when I look at it. He had been in the US Coast Guard during the war. I gave this to him many years ago for his birthday and ridiculously thought he might not recognize it.

I asked, "Do you know what this is?"
Dad: "Yup. Deck light."

Here is a variety of original ones: en.wikipedia.org/wiki/Deck_prism I think the big round one is called a melon. I have noticed flat grids of THICK glass in city sidewalks, lighting dank storage basements under commercial buildings. I wish I could see one from below. How to install a deck prism: www.youtube.com/watch?time_continue=17&v=-jbGrZMlViA