Traffic Light

A road signal for directing vehicular traffic by means of colored lights. The first use of lights to control traffic occured in 1868 in London street, where a revolving gas lamp with red and green glass was set up to help police constables direct horse-drawn traffic on a busy junction. The lamp, the concept of railroad engineer John Peake Knight (1828-86), exploded in January 1869, injuring its attendant constabable and the idea came to nothing. In detroit in 1920, early in the age of the automobile, William L. Potts (1883-1947), a police officer, invented a system of lights much closer to the traffic lights we know today. His idea was to adapt the red, green and amber lights used on railroads to control traffic on the highway, particularly at urban intersections. Within a year, the detroit authorities had installed fifteen. Around the same time, the Ohio inventor Garrett A. Morgan (1877-1963) came up with a semaphore-type traffic signal in Cleveland. His patent for the device was bought by General Electric Corporation and used as the basis for their traffic light monopoly. 

Today most traffic lights use the code of red for "stop", green for "go" and amber for "proceed with caution." In many countries, "running the red" is a criminal offence, but in others traffic lights are not seen as legally binding and are widely ignored. Urban myths regarding traffic lights include the untrue idea that in China red means "go", as it would be politically incorrect for it to mean "stop". The traffic light concept has even found applications outside of its original road safety purpose: the European Union has introduced a code system for food nutritional values based on the traffic light colors.