As the congestion of road networks continues to increase, the use of tunnels and underground passages is expanding with the aim of improving traffic flow and protecting the local environment from the impacts of increased traffic. Within tunnels, the reliability of lighting systems is crucial due to potential constraints on maintenance access and the prevalent corrosive atmospheric conditions.

Tunnel lighting systems are installed in road tunnels, underground passages, or beneath bridges, aiming to ensure vehicles can safely enter, pass through, and exit enclosed areas without impeding traffic flow. To achieve these goals, adequate illumination is required within tunnels to enable drivers to quickly adapt to the lighting conditions, identify potential obstacles, and pass through smoothly without the need for deceleration, while ensuring the same level of safety and visual comfort as approaching roads.

In lighting design, phased implementation schemes are typically proposed, covering aspects such as the selection of lighting sources, arrangement of luminaires, and variations in power, with the aim of meeting different lighting requirements for various stages of tunnel construction. It should meet the requirements of average road surface brightness, total uniformity of road surface brightness, longitudinal uniformity of road surface centerline brightness, and flicker and induction requirements. Currently, international lighting committees, such as the International Lighting Commission (CIE), and most countries around the world, formulate tunnel lighting standards based on brightness indicators.

The flicker frequency of the lighting system is related to factors such as lighting brightness, luminaire layout, and vehicle speed. Reasonable deter

mination of the flicker frequency can avoid visual discomfort and psychological interference, thus ensuring driving safety.

Induction refers to the inductive nature of lighting facilities, providing drivers with visual induction regarding the direction, linearity, and gradient of the road.

Five Key Areas of Tunnel Lighting:

According to the guidance from the International Lighting Commission (CIE 88-1990), the amount of light required inside the tunnel depends on the level of external light and the position where visual adaptation must occur inside the tunnel.

Entrance Zone: It is not inside the tunnel but the road section leading to the tunnel entrance. From this area, drivers must be able to see inside the tunnel to detect potential obstacles and enter the tunnel without deceleration. The driver's adaptability in the entrance zone determines the lighting level required inside the tunnel. The proportion of the transition stage should not exceed 1:3 because they are related to the human eye's ability to adapt to the environment and time. The end point of the transition zone is when the brightness equals three times the internal level.

Threshold Zone: The length of this area equals the "stopping distance." At the front of this area, the required brightness must remain constant and be related to the external brightness (L20) and traffic conditions. At the end of this area, the provided brightness level can quickly drop to 40% of the initial value.

Transition Zone: Within the distance of the transition zone, the brightness gradually decreases to reach the lighting level of the next tunnel section. One of the methods used by the International Lighting Commission to calculate visual adaptation is the L20 method, which considers the sightline within a 20° visual cone from the average brightness of the environment, sky, and road, centered on the driver's sightline starting from the entrance zone.

Internal Zone: This is the area between the transition zone and the exit zone, typically the longest area inside the tunnel. The lighting level is related to the speed and density of traffic, as shown in the table below.

Exit Zone: The part between the internal zone and the exit. In this area, during the day, the vision of drivers approaching the exit is affected by the external brightness of the tunnel. The eye can adapt almost immediately from low light to high light levels, so the process mentioned upon entering the tunnel is not reversed. However, in certain situations, enhanced lighting may be required, such as when the exit is not visible and the contrast between the front and rear of the driver needs to be enhanced, or in emergency situations or maintenance works where the exit serves as an entrance. The length of this area is up to 50 meters, and the lighting level is five times that of the internal area.

Types of Tunnel Lighting

Symmetrical and asymmetrical lighting is commonly used for the transition and internal areas of long tunnels, and for all areas of short or low-speed tunnels. Asymmetrical lighting can also be a way to enhance the brightness level in one direction of the tunnel.

Asymmetrical counter lighting is used to enhance the brightness level while emphasizing negative contrast of potential obstacles. Counter lighting is achieved through an asymmetric light distribution facing the traffic flow, both towards oncoming drivers and towards the direction of road travel. The light beam sharply stops when passing through the vertical plane of the luminaire. There is no light coincident with the direction of traffic flow, creating negative contrast and enhancing visual adaptation.

Forward counter lighting is sometimes required to enhance positive contrast, typically in the exit area where the exit is visible. In these cases, the asymmetric light distribution is similar to counter lighting, but in the same direction as the traffic flow, and is referred to as "forward counter." In dual-lane tunnels, counter lighting at the entrance can act as forward counter lighting at the exit. However, this technique is not recommended as the road brightness is very low, resulting in too great a difference between the exit area and the separation area.

Different requirements are set for tunnels of different lengths (from the International Lighting Commission - Tunnel and Underground Passage Lighting Guidelines).

When lighting tunnels, their length, geometric shape, and surrounding environment, as well as traffic density, must be considered.

Different lighting levels are set for each project:

The table below outlines some available installation options along with their respective advantages and disadvantages:

Ceiling Installation

Advantages:

Provides multiple or single row illumination, maximizing the utilization of lighting fixtures, keeping them unobstructed.

Achieves optimal efficiency and light distribution, avoiding glare issues.

Lower investment and maintenance costs, reducing operational expenses.

Light fixtures are concealed by signage, enhancing visual aesthetics.

Options include arched or framed types with or without ductwork.

Disadvantages:

Requires sufficient space away from the roadway to meet legal and safety standards.

Fixed fixtures are heavy, requiring additional work during installation.

In arched structures, additional engineering design and installation steps may be needed.

Improper positioning or obstruction may lead to glare issues.

Wall-Mounted Installation

Advantages 

Convenient for maintenance and replacement, requiring only one lane closure with minimal traffic disruption.

Lower investment and maintenance costs.

Easier access to luminaires as only one lane needs to be closed.

Disadvantages

Installation position may not meet minimum height requirements for legal and safety standards, posing safety risks.

Potential glare issues, especially when light is obstructed by vehicles.

Additional ductwork may be required when using arched structures, adding complexity to design and installation.

Insufficient space from the road may affect luminaire performance and light coverage

Key points of the tunnel intelligent lighting dimming system include collection module control technology, communication module control technology, and dimming module control technology.

Collection module control technology: The collection module, consisting of tunnel illuminance meters, flow detectors, and video detectors, is used to collect data required for lighting dimming. The system collects illuminance, working circuit voltage, and current parameters according to control requirements, converting analog signals into digital signals through wired RS-485 communication with the main control module, achieving precise lighting dimming.

Communication module control technology: The network transmission module, controlled by a local area network, achieves accurate and efficient data transmission, comprehensively monitoring the operating status of lighting facilities. The communication network between the main control module and the PLC control module is an optical fiber network or 4G/5G wireless network, executing, forwarding, and receiving commands through input ports to achieve intelligent dimming control.

Dimming module control technology: The intelligent lighting dimming system can be adjusted in real-time based on external environmental factors, reducing voltage, limiting current, and achieving automatic light adjustment and control. The system designs reference variables based on weather and traffic flow parameters to achieve energy savings and extend luminaire life. Additionally, preset control strategies are implemented based on different traffic volume levels to meet varying lighting requirements, achieving "on-demand lighting" and improving system operational efficiency through remote monitoring and management.

If you are still looking for suitable tunnel lights for your project, you can refer to our tunnel light series. Different tunnels and underground passages require different tunnel lighting configurations. Kinlights provides tunnel lighting solutions, offering flexible tunnel lighting systems tailored to your specific project requirements.