Knowledge about traffic lights

At the earliest, traffic lights only had two colors, red and green. Later, after improvement, a yellow light was added. The red light means stop, the yellow light means preparation, and the green light means pass. The reason why these three colors are used as traffic signals is also related to people's visual structure and psychological response.

The human retina contains rod-shaped and three types of cone-shaped photoreceptor cells. The rod-shaped cells are particularly sensitive to yellow light, and the three types of cone-shaped cells are the most sensitive to red light, green light and blue light respectively. Because of this visual structure, it is easiest for humans to distinguish red from green. Although yellow and blue are also easy to distinguish, because the eyeball has fewer photoreceptors sensitive to blue light, it is better to distinguish between red and green. Traffic lights are not set arbitrarily.

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 Distinguish (red-green color blindness is a minority after all). In addition, color can also express some specific meaning, to express hot or violent, the strongest is red, followed by yellow. Green has colder and calmer connotations. Therefore, people often use red for danger, yellow for warning, and green for safety.