This is a replica Type 24M Corvington Longarm lamppost at the Northwest corner of Prospect Park.
When I do these on-site urban sketches, I often do a little Googling to see if there's any interesting history or trivia about the subject. I didn't expect to find so much information of New York City lampposts! There are multiple posts on the cool site Forgotten NY, a very, very comprehensive site run by a guy named Jeff Saltzman, and several others.
Gas streetlights were introduced in New York City in 1823, and electric ones follolwed in 1892. Once the technology stabilized in the late 1800s, lighting companies began to pay attention to the ornamental design. The original "Corvingtons" were cast iron, and the "long arm" style was found on wide avenues and boulevards, to place the fixture further out into the wide expanse. There were many other types of lampposts suited for narrower streets, sidewalks, intersections, et al, with names like the "Bishop's Crook", the "Classic Twin", the "Type G", the "Type F," and the "Reverse-scrolled Type F."
In the 20th Century, they began to be replaced by simpler, cheaper aluminum and steel poles, like the Deskey Cobra and then the Westinghouse MO-8 lampposts, and only a few of the original cast-iron poles still exist. But in the 1980s, a movement started to retrofit lampposts in some areas with retro replicas, like this one in Park Slope.
The term "Corvington" was apparently coined by Mr. Saltzman after a similar model he'd seen in a catalog, and it was adopted by other "street mavens," of whom there are apparently many. "Type 24M" is from a code number given to every type of streetlamp in use by the NYC Bureau Of Gas and Electricity in The System Electric Companies: Photographs of Street Lighting Equipment As Of November 1, 1934. This is what I love about the internet. There are nerds for everything. No matter how particular or esoteric the subject, there is someone out there who is fiercely passionate about it, and they will build a website about it.