As you can see this fixture is connected to a spanwire that crossed this intersection. A pulley can be seen right above the fixture. This allowed the lamp to be serviced via lowering it down to street level via a winch that was on an adjacent pole. This was a very popular method of supporting and maintaining the arc lights that were used in previous decades. The earliest type ("open arcs") (1880s-1890s) required daily attention to their carbon rods. By the 1890s "enclosed arcs" came on the scene which were more efficient and required arc rod servicing only every 7 to 10 days. About 1912, lighting technology had advanced to the point that tungsten (filament) lightbulbs quickly rendered the old carbon arcs obsolete. In some instances their fixtures were altogether removed and replaced by then-modern luminaires like you see here. The tungsten bulbs typically lasted several months and provided much more light per watt than the previous arc lamps.