Why so many historic Philadelphia street lamps are shaped like the letter 'P'

PHILADELPHIA - Anyone walking down the cobblestone streets of Society Hill or Old City has likely spotted them: dark cast-iron lamp posts curving gracefully at the top into an arch resembling a capital letter "P." While locals often call them "P for Philly," the fixtures perched inside those curved brackets carry a direct link to one of the city's most famous innovators.

Known formally as "Franklin lights," the four-sided lanterns are modern tributes to a colonial-era fix that changed how cities lit the dark.

WATCH: Tyler Thrasher breaks down the backstory of Franklin street lamps

The colonial spark at Clifton's Alley 

The backstory:

Philadelphia's public lighting story began in 1751, when a resident named John Clifton mounted an oil lamp outside his two-story brick home at Second Street and Clifton’s Alley, an area later known as Drinker’s Court in modern-day Society Hill. It is widely recognized by historians as the first outdoor public street light in the city, according to Historic Towns of America.

Clifton’s light showed neighbors and city leaders how illuminated walkways could deter nighttime crime and help pedestrians navigate unpaved, muddy roads after dark. However, the technology used at the time had serious drawbacks.

Franklin's four-pane breakthrough 

Dig deeper:

The street lamps commonly imported from London were closed glass globes. Because they had no proper airflow, smoke from the oil and wicks quickly covered the inside with thick soot, dimming the flame and requiring constant cleaning. Worse, the round glass was fragile; if a stray stone or carriage wheel struck it, the entire globe shattered and the whole light was ruined.

Benjamin Franklin saw the problem and devised a practical solution. Instead of a single round bulb, Franklin built an enclosure using four flat panes of glass set in a metal frame. He added air crevices at the bottom and a chimney-like funnel at the top. The draft pulled air in from below and funneled smoke out the top, keeping the glass clear and bright.

Franklin's design also solved the maintenance issue: if an accident broke the lantern, workers only needed to slide in a single flat pane of cheap replacement glass rather than replacing an entire fixture.

Why the design endures

Big picture view:

Franklin went on to advocate for public street sweeping, paving and lighting legislation through the Pennsylvania Assembly in the 1760s, helping Philadelphia become the first American city with coordinated public street lighting.

During mid-20th-century preservation efforts, hundreds of reproduction Franklin-style lanterns mounted to the iconic curved posts were installed throughout historic neighborhoods. Today, the combination of Franklin's four-pane ventilated lantern and the distinctive curved bracket remains one of the city's most recognizable streetscape traditions.

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