This is a Light Director for Kessil A360/380 Refugium Lights. It fits 4" diameter Kessil lights, to concentrate the spread of light to your refugium instead of into your skimmer or other sump chambers.
This should just be installed on the plastic trim of the light- do NOT slide it up further and cover the ventilation holes.
Made here in the USA, by a college-student reefing hobbiest.
@HarrysAquatics