The traffic light is a signal light that controls the traffic operation, generally consisting of red light, green light and yellow light. The red light means stop, the green light means the pass, and the yellow light means the warning and observation.
Origin of traffic lights:
In 1858, red and blue mechanical wrench-type signal lights with gas as the light source were installed on the main streets of London, England, to direct the passage of carriages. This is the first traffic light in the world. In 1868, British mechanical engineer John Peake Knight installed the world's first gas traffic light on the square in front of the Houses of Parliament in Westminster, London. It consists of red and green two rotating square glass lanterns, red means "stop", and green means "attention". On its 23rd day of operation, a gas light suddenly exploded, killing a policeman on duty on the spot, and it was canceled.
In 1914, the traffic lights for electrical activation appeared in the United States. This traffic light consists of red, green and yellow circular light projectors installed on a tower on 5th Street in New York City. The red light means "stop", and the green light means "pass".
In 1918, controlled traffic lights and infrared traffic lights appeared. Controlled traffic lights, one is to install the pressure detector underground, and the vehicle will turn green as soon as the vehicle approaches the red light; the red light turns to green. Infrared traffic lights When pedestrians step onto pressure-sensitive pavement, it can detect that someone is about to cross the road, and the infrared beam can extend the red light of the signal light for a period of time, delaying the release of cars, so as to avoid traffic accidents.
The emergence of signal lights enables effective traffic control, which has obvious effects on dredging traffic flow, improving road capacity, and reducing traffic accidents. In 1968, the United Nations "Road Traffic and Road Sign Signaling Agreement" stipulated the meaning of various signal lights. A green light is a pass signal, and vehicles facing the green light may go straight, turn left and turn right, unless another sign prohibits a certain kind of turn. Vehicles turning left and right must give priority to vehicles that are legally in the intersection and pedestrians crossing the crosswalk. A red light is a stop signal, and vehicles facing a red light must stop behind the stop line at the intersection. The yellow light is a warning signal. Vehicles facing the yellow light cannot cross the stop line, but the vehicle can enter the intersection when it is too close to the stop line and cannot stop safely. Since then, this regulation has been used all over the world.
Why are traffic lights red, yellow and green?
The traffic lights are not set up carelessly but have a scientific explanation as well. At first, there were only two colors, red and green. Later, after improvement, a yellow light was added. The red light means stop, the yellow light means preparation for stop, and the green light means pass. The reason for using these three colors as traffic signals is also related to people's visual structure and psychological response.
According to the optical principle, red light has a long wavelength, has a strong ability to penetrate the air, and is more noticeable than other signals. Therefore, as a signal for prohibition of passage, green is used as a notification signal because the difference between red and green is the largest, and it is easy to determine (red-green color blindness is a minority after all).
In addition, color can also express some specific meanings, to express hot or violent, the strongest is red, followed by yellow. Green has a colder and calmer implication Therefore; people often use red for danger, yellow for warning, and green for safety.