Definately looks like an HPS retrofit for HX MV ballasts. The arc tube is longer and fatter than a typical 150w HPS. The coil wrapped around it is a starting aid to make up for not having the high voltage pulse ignitor. A bimetal contact disconnects it as the lamp warms up. I bet it starts out neon red instead of xeon white when first turned on
That's kinda cool. I think it's interesting how many Norelco security lights came with retrofit lamps. First was the old ballast-less ones with SBMV lamps, than this MV fixture with an HPS retrofit lamp.
Come to think of it, my first Norelco fixture came with a Sylvania Unalux HPS retrofit lamp (unfortunately broken ). I thought it was just something the previous owner had put in it, but after seeing this, I'm thinking it may have originally came with that bulb. The construction of it is consistent with mid-late 70s Sylvania BT28 lamps.
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Come to think of it, my first Norelco fixture came with a Sylvania Unalux HPS retrofit lamp (unfortunately broken