Tunnel lighting plays an important role in safety on the road, as the open road has a higher level of luminance than in a tunnel. Thus, critical lighting requirements are essential for the comfort of drivers eyes in adapting from outside luminance.
Things to consider
Research Local Standards
Not all tunnel designs are the same in terms of lighting application, therefore it is essential to know the local standards required, before anything else for tunnel lighting applications.
Concrete Tunnel Plan
It is important to identify the actual requirements for the overall tunnel project – are there existing luminaires? Or, does it need a new set of lighting? The prior might seem easier, but it is possible that further challenges may arise in the future.
Overall, having a concrete plan of which lights are required, and how they are to be installed takes time and knowledge, so it is important to ensure that all angles are covered.
Stages of Tunnel Lighting
Four parts of a tunnel need different levels of lighting requirements, that includes:
Threshold zone
In this zone, no objects are visible to the driver’s eyes due to high outside luminance. Special lighting is necessary for visual reliability to keep everyone safe. Eye adaptability changes over time while approaching the other parts of the tunnel.
The distance of this zone is from the entrance of the tunnel toward the stopping distance. Proper lighting will make any obstacle more visible then.
Transition zone
Upon entering the transition zone the luminance level will decrease gradually, and human eyes can easily adapt to this zone of the tunnel. It is 10 meters away from the tunnel entrance, enough for vision adjustment.
Interior zone
The Interior zone does not require eye adaptation anymore due to the constant luminance level in the zone. It is right before the exit zone.
The amount of lighting in this zone is still different from open road lighting, especially at night. It also depends on the size of the tunnel. Longer tunnels require a higher luminance level than short tunnels. Other factors that may cause low visibility are the exhaust fumes coming from vehicles. With that, a higher luminance level is advisable.
Exit zone
Obstacles are clearly seen in this zone with a low to a high level of luminance. The downfall would be at night on which there is that opposite feeling when entering the tunnel. The open road will appear as a black hole from the tunnel exit, and the best solution is placing along with road lighting. This helps drivers eyes to gradually adapt.
Luminance Level
We have mentioned the “luminance level” several times that differ in every stage of the tunnel. Apart from that, it also applies to the walls of the tunnel to help drivers distinguish possible obstacles.
Tunnel projects must ensure every spot of the tunnel is well-lighted in a uniform ratio. The illumination level at night is different from daytime, thus emergency lighting must be added.
The threshold zone has the highest luminance level due to the open road to the lighting transition. There will be a smooth luminance reduction towards the stopping distance. Luminance level is not highly necessary in interior and exit zones, except at night.
Another factor that affects luminance in the tunnel is the glare rating around 6 and 20 percent. It must be reduced to maximize visibility inside the tunnel especially in the threshold zone.
40m Length Rule
40 meters is the critical length of a tunnel around the world. Daylight enters the tunnel up to 15 meters. The lighting design is applied to the remaining 25 meters of the tunnel. This rule only applies to straight level tunnels.
Lighting Maintenance
Tunnel lighting may weaken in function from time to time, and so maintenance is essential. They should be checked regularly to prevent possible accidents in the tunnel due to improper lighting setup.
Final Words
In conclusion, lighting up a tunnel demands greater knowledge of the factors that may affect the driver’s safety. It includes the right luminance level in every part of the tunnel. The goal is to keep drivers aware of any obstacles upon entering and exiting the tunnel.