A complete explanation of tunnel lighting standards: How to ensure driving safety?

1. Why is tunnel lighting so important?

Tunnels are a special type of traffic space. Due to their closed structure, they lack natural light and are therefore highly dependent on lighting. When a vehicle enters a darker tunnel from a bright outdoor environment, the driver will experience a brief "black hole effect" and the eyes will not be able to adapt to the light changes immediately, making it difficult to identify the road conditions ahead and posing a high risk of accidents. When exiting a tunnel, if the external light is strong, a "white hole effect" will also be formed, making it difficult for people to see the external environment for a while. If these visual adaptation problems are not handled properly, they can easily lead to safety hazards such as rear-end collisions, collisions, or missing emergency signs. Tunnel lighting also plays a role in guiding driving direction, highlighting road structures, and identifying obstacles and emergency equipment. Reasonable lighting design is not only about improving visibility, but is also a core factor directly related to driving safety, traffic efficiency, and emergency response.

2. Design goals and basic principles of tunnel lighting

The design of tunnel lighting is not as simple as "installing lights". It needs to take into account functionality, safety, economy, and technical feasibility. The first is visual continuity. When the driver travels through different lighting environments, the field of vision must maintain a smooth transition to avoid discomfort caused by sudden changes. Secondly, the reasonable configuration of illumination and brightness. Different tunnel sections (entrance, adaptation section, basic section, exit) have different lighting requirements, which should be scientifically set according to traffic flow, vehicle speed and tunnel length. Illumination uniformity is another key principle to avoid local darkness or brightness, which will affect the driver's judgment of distance or object outline. Anti-glare design must be considered, and direct light should be controlled by lamp angle and sunshade to avoid interference to the driver. Energy saving is also an important goal of modern lighting system design. High-efficiency lamps should be used as much as possible and intelligent control systems should be introduced to achieve optimal energy utilization and operating cost control.

3. Summary of common tunnel lighting standards at home and abroad
Different countries and regions have formulated corresponding tunnel lighting standards based on their road characteristics and climatic conditions. my country's "Highway Tunnel Ventilation Lighting Design Specifications" (JTG/T D70/2-01) proposes the concept of segmented lighting, including entrance section, adaptation section, basic section and exit section. The illumination of each section is dynamically adjusted according to day and night, traffic volume and vehicle speed. In Europe, CIE (International Commission on Illumination) proposed the "L20 method", which is to calculate the external brightness that the driver can see from the perspective of 20 meters away from the tunnel, and determine the lighting intensity of the tunnel entrance section accordingly. The US FHWA emphasizes the relationship between the lighting system and traffic safety behavior, and advocates that the illumination should be designed based on the adaptability of the human eye, psychological comfort and vehicle operation dynamics. Although these standards are different in details, they all take driving safety, energy consumption control and equipment maintenance as their core goals. For designers, a deep understanding of the standards can not only meet regulatory requirements, but also help improve project quality and sustainability.

4. Detailed explanation of key technical parameters: illumination, brightness, uniformity
The performance evaluation of tunnel lighting systems relies on multiple technical indicators. Illuminance (Lux) is the most basic unit, measuring the luminous flux received per unit area. The tunnel entrance section usually requires high illumination (such as 500-1000 lux), while the basic section can be reduced to 50-100 lux, which is sufficient for normal driving. Brightness (cd/m²) is closer to human eye perception, representing the light intensity seen from a certain direction, and is a key indicator for designing "visual comfort". Lighting uniformity is divided into total uniformity (U0) and longitudinal uniformity (U1). The former is the ratio of the minimum to the average illuminance, and the latter is the balance of illuminance changes at consecutive points. Balanced lighting can reduce the fatigue caused by frequent eye adaptation. The glare index (GR) is used to evaluate the interference of light on the driver's vision. Excessive glare will cause people to miss traffic signs or obstacles, and must be controlled within the standard value (generally GR≤40). Combining these parameters and conducting simulation analysis in combination with the actual environment is a necessary link to ensure the lighting effect.

5. How to improve driving safety through lighting?
Scientific lighting has a direct and significant effect on ensuring tunnel traffic safety. Through reasonable illumination design and lamp arrangement, drivers can begin visual adaptation before entering the tunnel, reducing the discomfort caused by the black hole effect. In the tunnel, uniform and stable lighting allows drivers to clearly judge the distance to the vehicle in front, lane boundaries and sudden obstacles, so as to respond in time. Modern tunnels are increasingly introducing intelligent lighting systems, which can automatically adjust the light intensity according to traffic volume, external weather, and time period, saving energy without affecting visibility. High-color LED lights can effectively improve color discrimination, making it easier for drivers to identify warning signs and emergency passage directions. In addition, reasonable exit lighting alleviates the white hole effect, allowing drivers to transition more naturally from darkness to strong light environments. The combination of these measures not only improves driving comfort, but also fundamentally reduces the accident rate, especially in multi-bend tunnels, long-distance tunnels, and high-frequency traffic scenes.

6. Application trends of LED and intelligent control technology
In recent years, the field of tunnel lighting is rapidly transforming from traditional sodium lamps to LED technology. LED lamps have the advantages of high energy efficiency, long life, and fast response, and can save more than 60% of energy compared to traditional light sources. More importantly, LEDs can achieve precise dimming, providing a basis for intelligent control. The currently widely used adaptive lighting system can adjust the light intensity in real time through sensors or central control systems, such as automatically optimizing the lighting level according to vehicle speed, traffic density, or weather changes. In addition, LED modules are highly integrated, easy to maintain and replace, and more suitable for segmented control and remote monitoring. Some advanced tunnels are equipped with intelligent technologies such as environmental sensors, video analysis systems, and remote fault diagnosis functions, making the entire lighting system part of traffic management. With the development of the Internet of Things and 5G technology, tunnel lighting will develop in a smarter, greener, and safer direction in the future, becoming an important part of smart transportation infrastructure.