Although streetlights have been associated with cities for more than a thousand years, they are rarely considered for functions other than luminary purposes. One of the distinct features of streetlights is their geographic location. In particular, streetlights follow the roads and streets that are the arteries of the city, and at night they outline the city so it can be seen from many miles away.
As global urbanization trends continue, more people will move to the city. It is estimated that by the year 2050 more than 75% of the world population will live in cities. As a result, more streetlights will be needed to keep pace with expansion of a city and to provide ubiquitous lighting coverage for the population. The first challenge will be the huge amount of energy consumption. Street lighting consumes a good part of the 19% of power currently used for all lighting with a carbon footprint corresponding to burning billions of trees. Saving power for lighting has been an inspiration for technical advances and innovations and we have been advancing rapidly from incandescent, fluorescent, and high-pressure sodium lights to LED lighting.