"Stop when the light is red, go when the light is green, and wait when the yellow light is on." This is a traffic rule that everyone has learned and obeyed since childhood. However, few people think about why traffic lights are composed of three colors: red, yellow, and green. Instead of using other colors?
In fact, traffic lights first appeared in Britain in the 19th century to reduce the occurrence of horse-drawn carriage accidents. The gas signal lights used at that time not only required manual operation to change colors, but were also extremely unstable. It was not long before they were deactivated due to explosions. Then in 1914, in Cleveland, USA, signal lights reappeared in the form of electric lights. Around 1918, Hu Ruding, a Chinese scholar in the United States, suggested adding a yellow light to serve as a reminder before changing lights.
So, why are the three colors of red, yellow and green the most suitable colors for traffic lights?
Human visual function structure
The human retina contains rod-shaped and three types of cone-shaped photoreceptor cells. Rod cells are extremely sensitive to yellow light, and the three types of cone cells are sensitive to red light, green light and blue light respectively. Therefore, humans can easily distinguish between red and green. Although yellow and blue can also be distinguished, the eyeball itself has fewer photoreceptor cells for blue light, so it is not used for safety reasons.
People's psychological reactions to colors
Red has the strongest feelings and is often used to represent prohibition or danger. Moreover, the red light has strong penetrating power and is easily visible even on cloudy, rainy or foggy days. Yellow is a soft, warm color that can bring a slowing down and buffering visual effect to people, and plays a role in signaling people's anticipation. Green belongs to the cold color system, which can calm people's hearts and often represents safety and peace, so it can represent passage.
