Why should the traffic lights be set with these three colors?

According to the optical principle, red light has a long wavelength and strong ability to penetrate the air, which is more noticeable than other signals. It is used as a signal to prohibit traffic, and green is used as a notification signal because red and green are the most different and easy to distinguish (red and green color blindness is a minority after all). In addition, colors can also express some specific meanings. Indicates heat or intensity, the strongest is red, followed by yellow. Green has a colder and calmer meaning. Therefore, people often use red for danger, yellow for warning and green for safety.

Extended data:

1858, red and blue mechanical wrench signal lights with gas as light source were installed on the main streets of London, England, to direct the passage of carriages. This is the earliest traffic light in the world. 1868, British mechanical engineer knight installed the world's earliest gas traffic lights in the square in front of Westminster Parliament Building in London. It consists of red and green lanterns and rotating square glass. Red means "stop" and green means "pay attention". On the 23rd day of its operation, the gas lamp suddenly exploded, and a policeman on duty died on the spot, so it was cancelled.

19 14, electric traffic lights appeared in the United States. This traffic light consists of red, green and yellow circular projectors, which are installed on a tower on Fifth Avenue in new york. The red light means "stop" and the green light means "pass".

19 18, traffic lights with control and infrared traffic lights appeared again. There are controlled traffic lights, one is to put the pressure detector underground, and the vehicle will turn green as soon as it approaches the red light; The other is to start the traffic lights with a loudspeaker. When the driver meets a red light, he presses the buzzer to turn the red light into a green light. Infrared traffic lights When pedestrians step on the pressure-sensitive road, they can detect that someone is going to cross the road. Infrared beam can prolong the red light of traffic lights for a period of time, delay the release of cars and avoid traffic accidents.

The appearance of traffic lights can effectively control traffic, which has obvious effects on diverting traffic flow, improving road capacity and reducing traffic accidents. 1968 "United Nations Agreement on Road Traffic and Road Signs" stipulates the meanings of various traffic lights. The green light is a traffic signal. Vehicles facing the green light can go straight, turn left and turn right unless another sign prohibits a turn. Vehicles turning left and right must give priority to vehicles legally driving at intersections and pedestrians crossing crosswalks.

The red light is a signal that no traffic is allowed. Vehicles facing the 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 they can enter the intersection when they are too close to the stop line to stop safely. Since then, this provision has been widely applied in the world.

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