City Lights by Kimberly

At dusk and dawn, millions of street lights are turned on and off throughout the world. Everyday many of them by the light of the sun itself.
Most lights are controlled by time switches, which operate a group of lights in neraby streets. The earliest time switiches worked by clockwork and had to be wound up and adjusted every week.
Many modern time switches now have an electric clock with a rotating dial containing levers or tappets, which turn the lights on or off at the chosen time. They are similar to many time switches on central-heating systems.
Recently street-lighting engineers have developed a photoelectric control unit called a "pecu" which is the electric supply to lights.
At dawn, light falling on a photocell causes electrons to flow from on atom to another, conducting electricity to the switch and turing it off. When darkness falls, the electrons become immobile and the current stops and the lights turn on. So, next you take a look at a street light just know that they too have a story.