There was a question about lighting below a deck on the Greenbuilding list. The question was about using polycarbonate as a decking material. It might have the strength, but I would be concerned about the slip-resistance of it as a walking surface.

But another alternative that occurred to me is a deck prism I got some years ago. Before there was electric lighting on ships, this was a way of bringing light belowdecks without using lamps (wooden ships plus fire – bad).

The prism is just a chunk of solid glass. To use it as a light, it would be set flat-side up into the deck surface, with the pointed prism end protruding through the ceiling. Light striking the top passes through the glass and is scattered throughout the space below by the six facets of the prism. The one I have is 4″ across, and has a lip on the base that would let it be set through a deck opening (1-1/2″ thick) and held in place while being flush with the deck surface.

For a contemporary wood deck, I’m sure it wouldn’t be hard to fabricate a frame of some sort to hold the prism in place at the right depth so that the top would be even with the deck. I’d cut half-hexagon notches in two adjacent deck boards, rather than trying to cut a hexagonal hole in a single board.

Amazon carries a version of deck prism that looks very much like the one I have for only $15. I’ve had the one I have for more than a decade, but it’s only been a desk ornament for me. I have always wanted to put it to actual use. This could be an interesting use for it.

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