These two parts form internal glare shields to improve the dark water performance of the stock LED's on the OpenROV 2.8 light board.The outer profile matches the O.D. of the end plates on the electronics frame, which gives a pretty small clearance with the I.D. of the acrylic tube. I might make them just a little larger, or experiment with some black foam gaskets, but so far, they seem to help a lot and I'm reluctant to scratch the inside of the acrylic tube. I will definitely also try some black felt on the front of the light board around the circular cutouts you can clearly see reflected in the second photo. They mount via the little screws that secure the light board to the camera board.
The photos are of a very dark hallway, with the internal lights at full bright. The second photo is with the glare shields installed. The first is without.
Make the bottom skin 1.0 mm, and it will print the flat parts solid. I used black ABS, though I'm not sure it gets hot enough in the ROV for PLA to be a problem. So, I would suggest any material, in black if you have it.
The glare shields themselves made a big improvement. But the face mask (black felt covering) between the LED's and the camera made a huge difference cutting down reflections from the shiny blue PCB. So I included it here as well.