rare all original and completely intact early 20th century reinforced concrete sidewalk solid "no. 4" standard square pendant glass prism

original well-preserved early 20th century antique american industrial 3-way "quickset" system reinforced concrete sidewalk "no. 4" square-shape pendant glass prism designed and fabricated by the american 3-way prism company, chicago, il. american 3-way was the result of a merger between the american 3-way prism company and the american luxfer prism company in the early 1920's. the company specialized in the fabrication of prismatic lights for pavements, floor, skylights, store fronts and so on. the solid glass pendant style sidewalk prism light was salvaged from downtown chicago during repair work performed by the streets and sanitation department. this type of vault or sidewalk light harnessed natural light from above to illuminate the otherwise darkened basement spaces that extended below the sidewalk.