Some of the earliest arc lights for street lighting applications in the US were like this one. It was commonplace to have two pintype insulators mounted on a cast iron bracket immediately below the fixture for the power supply wires. These early arc lights were of the "open" arc design. They required arc rod trimming maintenance every day or two. About when this photo was taken enclosed type arc fixtures for street lighting were introduced. They soon superceded the open-style variety on account of the fact they required arc-rod maintenance once every seven to ten days and were more energy efficient. Tungsten (filament) advancement commencing around 1912 led to the slow demise of arc street lamps. The former basically employed standard lightbulbs and were far less costly to operate and maintain.