These light fixtures were pretty common around Boston and its suburbs through the 1960s when they were replaced by mercury vapor ones. The fixture you see was among many that had the letters E.L. Co. within a round medallion within the scrollwork. It is assumed that the initials represent the Edwin Lewis Co. (of Boston) however that has not been proven. Edwin Lewis was a prominent distributor of electrical supplies. They were purchased by the Pettingell Andrews Company in the early 1920s.

Also note the crossarm stenciling, it stood for the Edison Electric Illuminating Company (of Boston). The name was changed to Boston Edison in 1938.