Check out EBay item # 2643 3785 3554. I remember seeing this advertised by Crouse-Hinds sometime in the early 1970’s.
It was an energy saving adapter for “high hats” that used 150 to 300 watt incandescent reflector bulbs. I have never seen a PAR 36, 75 watt mercury  lamp listed in any catalogs. Can someone identify this lamp? Or is this a proprietary lamp developed just for this adapter?