What is a tunnel light?

Tunnel lighting is an indispensable part of highway transportation facilities, Effective tunnel lighting is crucial for safety, comfort, and efficient traffic flow.and its design is not only related to driving safety and traffic efficiency, but also directly affects the energy consumption and maintenance costs of the lighting system. Reasonable brightness configuration and lamp arrangement, with intelligent control system and emergency lighting design, is the key to realize safe, efficient and green tunnel lighting.such as the "black hole effect" at the entrance and the "white light phenomenon" at the exit.

 

一、Lighting zoning and functional objectives

The tunnel lighting system is divided into the following zones according to the driver's visual adaptation characteristics and functions:

 

Section Name	Functional Objective	Design Intent
Entrance Zone	Suppress the "black hole effect"	High brightness for visual guidance, to ease adaptation from bright to dim.
Transition Zone	Smooth brightness transition	Gradually weaken lighting intensity, avoiding abrupt adaptation.
Interior Zone	Provide stable visual environment	Meet the minimum visual requirements for safe passage in the main part of the tunnel.
Exit Zone	Alleviate the "white hole effect"	Allow drivers exiting from dim conditions to adapt to external light in advance.
Approach Road	Transition for entering/exiting at night	Provide supplementary lighting for nighttime, enhancing driving comfort.

 

 

 

二、 design basis of brightness configuration

1. Brightness outside the cave L20 and entrance section brightness Lth: Lth = L20 × k

 

 Where: L20: brightness outside the cave (generally take 3000 cd/m², mountainous areas for the typical value);
k: discount factor, according to the traffic volume, the composition of models and years of operation to take 0.02 ~ 0.07.
Example: when L20 = 3000 cd/m², k = 0.037 → Lth = 111 cd/m².

 

2.Brightness Configuration Reference by Zone

 

 

Section Name	Luminance (cd/m2)	Length (m)
Entrance Zone 1	110~180	80~120
Entrance Zone 2	Half of the upper segment	80~120
Transition Zone 1	~16.7	100~140
Transition Zone 2	~5.55	100~140
Interior Zone	2.5~4.5	Depends on tunnel length
Exit Zone 1	7.5~13.5	30
Exit Zone 2	12.5~22.5	30
Tunnel Approach Road	≥2.0	185~255

 

 

三、 Traffic Volume and Luminance Reduction
     

        The setting of the luminance reduction factor (k) based on traffic volume is a crucial basis for achieving energy savings and rational lighting.

     

       When the travel time between two tunnels is less than 15 seconds, AND the passage time through the preceding tunnel is greater than 30 seconds, the luminance in the entrance section of the subsequent tunnel can be reduced by 25% to 50%. This optimization improves visual continuity and saves energy.

 

  

Traffic Scale	Recommended k-value	Application Scope
< 6000	0.02 - 0.035	Secondary trunk roads, low-traffic volume tunnels
6000 - 15000	0.035 - 0.05	General expressways
> 15000	0.05 - 0.07	Trunk expressways, high proportion of heavy vehicles

 

 

四、Luminaire Arrangement Design Principles and Refinements

        Luminaire arrangement is a crucial aspect of tunnel lighting system design. It not only relates to the uniformity of illuminance and luminance distribution but also affects light continuity, glare control, construction difficulty, and long-term maintenance costs.

 

Luminaires can adopt the following arrangement forms:

 

Symmetric Arrangement on Both Sides (Conventionally Recommended): Suitable for small and medium-sized single-bore tunnels. Provides uniform illuminance distribution and is convenient for maintenance.
 

Single-Side Arrangement (Special Cases): Used when ventilation or fire protection pipelines occupy space on one side. Corresponding lighting density needs to be appropriately increased.
 

Ceiling Centerline Arrangement: Applicable to special cross-sections or new LED linear luminaires. Conducive to glare control and spatial uniformity.
 

Continuous Strip Lighting: Used in long tunnels with high visual guidance requirements, can be paired with grilles or linear module light sources.
 

Sectional Mixed Arrangement: For enhanced sections/entrance/exit zones, dense symmetric arrangement is used; for the middle section, conventional spacing is adopted, saving investment.

 

The spacing of luminaires should avoid creating undesirable flicker effects. The design principle is as follows:

Determine the flicker frequency f (Hz) based on the design speed:f=s/v

 

 

Design Speed	Recommended Spacing (Single-Side)
80 km/h	≤ 12 m
100 km/h	≤ 14 m
120 km/h	≤ 15 m

 

 

For enhanced sections (entrance, exit): Recommended dense spacing is 6~10m. The basic section's spacing is generally 12~16m, comprehensively considered based on light distribution, reflectivity, luminous flux, and other factors.

 

Applications

Tunnel lights are critical in:

Road and railway tunnels.

Underground passages and subways.

Mining or industrial tunnels.

 

       In summary, a tunnel light is a robust, high-performance lighting fixture specifically engineered to overcome the unique visual and environmental challenges of tunnels, prioritizing driver safety, comfort, and energy efficiency.Tunnel lights are not just "lights in a tunnel" but a carefully engineered system tailored to human vision, safety requirements, and environmental conditions. They play a vital role in reducing accidents and ensuring smooth traffic flow in confined, low-visibility spaces.