Philadelphia is located at the confluence of the Delaware River and its tributaries in eastern Pennsylvania, on the river. This is the same as we have visited Lyon, France, is also a beautiful city was dressed in green water. Philadelphia has a population of fifth, which is the largest city in the United States, with a population of 1 million 600 thousand. The choice of Philadelphia as the object of investigation because Philadelphia has played a pivotal role in the creation of the United States, is a world famous historical city. 200 years ago, the United States was born here, it is proud of the symbol of the United states. Moreover, we are surprised to find that the history of the United States and the history of lighting are intertwined. After comparing the development of American cities with the development of lighting technology, we may see the nature of the city's lighting.
The longest street in the world uses high-pressure sodium lamp as the light source
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