The structure and shortcomings of traditional traffic lights

Traffic lights are a kind of traffic safety management facility. Traditional traffic lights are mainly composed of power supply, light source, lamp housing, reflective bowl (i.e. parabolic reflector) and colored light distribution mirror (i.e. colored lens), as shown in Figure 1. Among them, the light source is an incandescent lamp or a halogen tungsten lamp. The mains can directly power the incandescent lamp, while the halogen tungsten lamp needs to be converted by a transformer before it can be powered; the function of the reflective bowl is to collect the light emitted in all directions and emit it forward; the function of the colored light distribution mirror is to reasonably distribute the white light emitted forward to produce red, yellow and green light.

Figure 1 Basic structure of a traditional traffic light

Traditional traffic lights have the following unavoidable shortcomings:

First, the existence of the reflective bowl causes a false display effect. This situation mainly occurs in the early morning and evening. Since the angle between the direction of sunlight projection and the ground is small at this time, the edge of the signal light cannot block the sunlight incident on the signal light mirror. The incident sunlight passes through the colored light mirror of the signal light and is reflected by the reflective bowl before being emitted. In this way, although the signal light itself is not lit, from the perspective of drivers and pedestrians, it is like it is lit, so a false display effect occurs, which is easy to cause traffic accidents.

Second, the life span is short and the maintenance cost is high. Due to the harsh working conditions of traffic lights, such as frequent lighting, unstable voltage supply at night and high ambient temperature, the life span of the light source is much shorter than that under normal use conditions. Taking the commonly used incandescent lamp as an example, the life span of the incandescent lamp when used in traffic lights is generally only about 1500 hours, so the maintenance cost is very high. Although the price of the incandescent lamp itself is not high, it requires a high-altitude operation vehicle when replacing the lamp, and the labor cost is considerable.

Third, since colored lens are mostly made of plastic, they will change color to varying degrees under long-term sunlight exposure, generally fading, which will cause the color of the light to drift and easily increase the incidence of accidents.

Fourth, the power of incandescent lamps is usually 100-150W, and the power consumption is too high. Generally, a typical intersection needs to install 4 sets of motor vehicle signal lights and 8 sets of pedestrian signal lights. If 100W incandescent lamps are used as light sources, and each set of lamps is lit for 20 hours a day, the power consumption for the whole day is 24kW h. Calculated at 1 yuan/kWh for industrial or commercial electricity, the daily electricity fee is 24 yuan, and the annual electricity fee is 8,760 yuan. For a medium-sized city with 100 light-controlled intersections, the annual electricity fee for signal lights alone is 876,000 yuan, which is a considerable figure.