Tunnel lighting is an important part of tunnel traffic safety. Compared with general road lighting, tunnel lighting requires lighting throughout the day, and daytime lighting is more complicated than nighttime lighting. Tunnel lighting should not only consider that the road surface should have a certain level of brightness, but also should further consider the design speed, traffic volume, linearity and other influencing factors, and comprehensively evaluate the lighting effect from the aspects of driving safety and comfort, especially in tunnels. The entrance and its adjacent sections need to consider the process of human visual adaptation. At the same time, there are obvious differences between the visual phenomena in tunnel lighting and the visual phenomena encountered on the road. When the driver approaches, enters and passes through the tunnel from a bright visual environment during the day, it is easy to cause a variety of visual problems. Such as "white hole effect" and "black hole effect".
In the daytime, the visual phenomenon in tunnel lighting will show several characteristics
1.Visual problems before entering the tunnel. In daylight conditions, because the brightness outside the tunnel is much higher than that inside the tunnel, the driver will see the "black hole" phenomenon in the long tunnel and the "black frame" phenomenon in the short tunnel.
2.A visual phenomenon that occurs immediately after entering the tunnel. Entering from the bright outside into the darker tunnel, because the driver's vision has a certain adaptation time, he cannot see the inside of the tunnel immediately, resulting in "adaptation lag."
3.Visual problems inside the tunnel. Inside the tunnel, smoke is formed due to the accumulation of exhaust gas from motor vehicles. Tunnel lighting and car headlights are absorbed and scattered by the smoke to form a light curtain, which greatly reduces the brightness between the front obstacle and its background. Contrast, resulting in reduced visibility of obstacles.
4.Flicker effect. This is due to the improper arrangement of the lighting fixtures causing the uneven brightness distribution in the tunnel, which results in a periodic light-dark alternate environment, which will form a flashing feeling at a certain speed.
5. Visual problems at the exit of the tunnel. Suddenly coming from a very dark tunnel to a very bright tunnel exit will produce strong glare, which will make the driver of the vehicle unable to see the road conditions, which will lead to safety accidents.