As a special section of the tunnel, especially in the use of the tunnel, the external brightness of the tunnel changes greatly with time, and a series of visual problems will appear when vehicles enter and leave the tunnel. It can be roughly divided into the following two types: in the case of short tunnels, people see high brightness from the entrance to the exit, which will produce a "black box" effect; In the case of a long tunnel, when vehicles enter the tunnel, they will feel dark inside, unable to identify the situation near the entrance or even obstacles, resulting in a "black hole" effect. When a vehicle approaches the exit of the tunnel and sees a dazzling white hole, it will form a "white hole" effect, which will also reduce the visual function and visual comfort of the driver when he leaves the hole, and it is impossible to accurately judge the vehicle in front. The same is true when approaching the exit through the tunnel at night, which will produce a "black hole" effect.