With the development of various transportation and the need of traffic command, the first truly three-color lamp (red, yellow, green three symbols) was born in 1918. It is a three-color round four-colour projector, installed in New York City, Fifth Street, a high tower, because of its birth, the city traffic greatly improved.
The inventor of the yellow signal lamp is our country's Hu Ruding, he with "Science saves the Nation" ambition to the United States to further study, in the big inventor Edison as chairman of the United States General Electric Company incumbent. One day, he stood at the bustling crossroads waiting for the green signal, when he saw the red light and was about to pass, a turn of the car to wipe his body, scared him a cold sweat. Back to the dormitory, he pondered, finally thought in the red, green light plus a yellow lights, reminding people to pay attention to danger. His proposal was immediately affirmed by the parties concerned. So red, yellow, green tri-color signal is a complete command signal family, all over the world land, sea and air transportation.