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Traffic Light
Aug 30, 2013


At the crossroads, there are traffic lights in red, yellow, green and three colors hanging on all sides. It is a quiet traffic policeman. Traffic lights are internationally accepted traffic lights. The red light is the stop signal, the green light is the pass signal. At intersections, cars coming in several directions are brought together here, some are going straight, some are turning corners, and who is going to go first. That is to follow the traffic light command. The red light is on and the vehicle is allowed to make a right turn without obstruction of pedestrians and vehicles; the green light is allowed to allow the vehicle to go straight or turn; the yellow light is on and stops at the stop or pedestrian crossing; When the yellow light flashes, warn the vehicle to pay attention to safety.

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Light color

The earliest time only red and green colors, and later improved, adding a yellow light, stop the red light, the yellow light indicates that the green light means the passage. The reason why the three colors are used and the traffic signals of these three colors are also related to people's visual structure and psychological reaction.

The human retina contains rod-shaped and three cone-shaped photoreceptors, which are particularly sensitive to yellow light and the three cone-shaped cells are the most sensitive to red, green and blue light, respectively. Because of this visual structure, people are the easiest to distinguish between red and green. Although yellow and blue are also easy to distinguish, but because the eye sensitive to blue light sensitive cells less, so distinguish the color, or red, green is better.

Traffic lights are not free to set.

Scientific basis

According to the optical principle, the wavelength of the red light is long and penetrates the air

Strong and more attractive than other signals. Therefore, green is used as a forbidden signal because it has the largest difference between red and green and is easily distinguishable (red, green and white are, after all, a minority). In addition, the color can also express some specific meaning, to express the hot or dramatic words, the strongest is red, followed by yellow. Green is colder and calm meaning. Therefore, people often represent the danger in red, yellow on behalf of the warning, the green represents safety.

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Development History

In 1858, red and blue mechanical wrenches were installed on the main streets of London in the United Kingdom to direct the use of coal gas as a light source. This is the earliest traffic light in the world. In 1868, British mechanical engineer Nayette installed the world's first gas traffic light on the square in front of the parliament building in Westminster, London. It consists of red and green two rotating square glass lanterns, red, "stop", green, "attention." On the 23rd day of its operation, the gas lamp suddenly exploded and one of the police officers was killed on the spot and was canceled.

In 1914, an electrically activated traffic light appeared in the United States. This traffic light consists of a red, yellow and green round light projector mounted on a tower on 5th Avenue in New York City. Red light means "stop" and green light means "pass".

In 1918, another traffic lights with control and infrared traffic lights appeared. Traffic lights with control, one is to put the pressure detector in the ground, the vehicle becomes a green light close to the red light; the other is to use a megaphone to start the traffic light, the driver hit the red light when the horn, so that The red light turns green. Infrared Traffic Light When a pedestrian embarks on a pressure-sensitive road, it can detect that someone is crossing the road. The infra-red beam can prolong the red light of the traffic light for a period of time and delay the release of the vehicle so as to prevent a traffic accident.

The emergence of signal lights, traffic control can be effective for the ease of traffic flow, improve road capacity, reduce traffic accidents have a significant effect. In 1968, the UN Agreement on Road Traffic and Road Signs signals the meaning of various lights. The green light is a traffic signal and the vehicle facing the green light can go straight, left and right, unless the other sign prohibits a certain turn. Vehicles turning left and right must give priority to vehicles that are legally traveling in the intersection and pedestrians crossing the pedestrian crossing. The red light is a forbidden signal, and the vehicle facing the red light must stop after the stop line at the intersection. The yellow light is a warning signal and the vehicle facing the yellow light can not cross the parking line, but the vehicle is very close to the parking line and can not enter the intersection safely. Since then, this provision has become universal in the world.

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The Shaanxi Yiyuan Traffic Technology Engineering Co.Ltd. 

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  • Shaanxi Yiyuan Traffic Technology Engineering Co.,Ltd

    Tel: +86-29-88270591

    E-mail: sxyyjt@sx-yyjt.com

    QQ: 1829090767

    Zip: 710065

    Address: No.5, Production Road, West Thermal Power Plant, West Section Of Hongguang Road, Weiyang District, Xi'an, Shaanxi, China


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