My Grandmothers Lamp

I really don't know much about this lamp. My mother says she remembers it being on her mother's porch when she was a little girl. I am guessing that makes it circa 1920's. My grandmother's house was in Chicago, IL which I have been told was a major distribution point for lamps in the 1920's. I don't know much about lamps, so any information like category, style, age, manufacurer, etc. would be helpfull.