Interesting mercury floodlight fitting (Philips DHF016)

Found in the grounds of a building today. Judging by the colour of the lamp's arc tube it is toast and clearly hasn't worked in a number of years! Shame, because clear-fronted mercury reflectors are rare and are quite uncommon. Interestingly the fitting has a label inside stating "PAR lamps" or something along those lines, so maybe the lamp is an even rarer self-ballasted version? Try as I might I cannot see any type of filament so I would assume there is a remote ballast located somewhere.