The tunnel’s unique structure, as well as the physiological structure of the human eye, dictate this. The brightness difference between the inside and outside of the tunnel is significant since it is a semi-enclosed construction. The human eye must adjust to the time when a vehicle enters or departs the tunnel. This is known as “adaptation lag.” People’s visual responses lag when cars enter the cave during the day owing to the rapid reduction in brightness, creating a “black hole effect” that makes it impossible to differentiate the situation in the cave; when the vehicle departs the tunnel, a “white hole effect” forms, generating extreme glare.

To avoid an excessive difference in light intensity between inside and outside the tunnel, as well as a short-term visual obstruction to human eyes, the LED lights at the tunnel’s entrance and exit must be dense, reducing the light intensity difference between the outside and inside of the tunnel during the day and ensuring the driver’s safety.