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When driving in tunnels, the words "dark and dingy" comes to mind to describe the passages. They are poorly illuminated and one gets the feeling that an accident can happen at any given time. This is why when you see a tunnel that is well illuminated, you may ask yourself "why are all tunnels not well lit?"
LED lighting shows us that tunnels, like exterior spaces, can be brightly lit at all times. In fact, tunnels that are lit by LEDs help drivers’ eyes to adjust easily and quickly. The passages don't have disruptive maintenance. Energy usage is low with better light quality.
One of the biggest challenges of tunnel and underpass lighting is supporting drivers’ visual acuity day and night – from the entry to exit. Good tunnel lighting creates consistent light levels throughout the tunnel for safe passage.
Tunnels happen to be corrosive environments that need durable and sealed luminaires. Heavy traffic and weather expose the lights to exhaust, salt, and corrosive elements.
LED tunnel lighting is the best lighting option for tunnels. To begin with, the lights have a power efficiency of 75% or more. Meaning they use 75% less energy than traditional lights. Second, their shortest lifespan is 50,000 hours. High-quality LED tunnel lights can function for up to 100,000 hours.
Some of the LED lights used in tunnels have a beam angle with a horizontal axis of 100° and a vertical axis of 90°. The luminaires distribute light using a beam pattern and the input voltage is 100-277V AC.
Advanced technologies and materials are used in the manufacture of LED tunnel lights. Manufacturers use such measures because LED lighting is nothing like normal road lighting. For example, tunnel lighting gets affected by the environment such as vibrations, noises, and exhaust fumes.
It's important for manufacturers to discuss designs for new tunnels to create the best lighting system. To make the structure safe for drivers, pedestrians, and even cyclists.
Tunnel Lighting Lux Level
If a tunnel’s total length is 736 meters, it may be divided into 3 illumination areas for lighting purposes. The brightest area is the area between the entrance to 30 meters inwards. A total of 80 lux is needed in this area for adequate illumination.
The area next to the brightest area (30-60 meters inwards) is the medium bright area and requires about 50 lux. 40 lux may be needed in the area after that (60-96 metres inwards) which is known as the transition area. The middle of the tunnel does not need bright light, approximately 30 lux.
In a tunnel of this size, only 143 luminaires may be needed for the whole structure. The entrance and exit of the tunnel can use 40 units each and the remaining 63 pieces installed in the middle. They can pair with intelligent lighting controls to adjust the brightness with the natural light.
It is worth noting that the design of a tunnel will be the biggest determinant of the fixtures required. Since not all tunnels are straight. As a LED tunnel lighting manufacturer, lights can be designed to meet your specific requirements.
Zones of Tunnel Lighting
The International Commission on Illumination (CIE) is a governing body on the art and science of lighting. They have a publication on tunnel lighting (CIE 88-1990) that states:
the quantity of light required in a tunnel is directly dependent on the available natural light outside the tunnel. Also, the point in the tunnel where the user's visual adaptation must occur.
When it comes to planning the lighting design of a tunnel, there are 5 important areas to consider.
1. Access Zone
This area is not found within the tunnel, it is actually the stretch of road that leads to the tunnel’s entrance. When at this zone, drivers must be able to see the tunnel’s interior and detect any possible obstacles. They must be able to drive easily into the tunnel without reducing their speed.
The capacity of the driver to adapt in the access zone dictates the lighting level in the subsequent part of the tunnel. One method used by the International Commission on Illumination to compute visual adaptation is the L20 method. The method takes into consideration the median luminance from the road, sky, and the environment in a cone of 20° centered on the driver's line of sight from the start of the access zone.
2. Threshold Zone
This is the part of the tunnel that is visible before a driver drives into the tunnel. The length of this zone is equal to the stopping distance. The required luminance for the first part of this zone must always remain constant as it is linked to the luminance for the exterior (L20) as well as traffic conditions. At the end of the threshold zone, the luminance level should be decreased to 40% of the value.
3. Transition zone
This zone comes after the threshold zone and is where the luminance level goes down to the level in the inner zone. The luminance in this zone is necessary for drivers to be able to see the stopping length in front from any point in the transition zone and the threshold zone.
Over the distance of this zone, the luminance is decreased progressively to meet the level in the inner zone. The decrease stages should not surpass a ratio of 1:3. This is because they are connected to the eye's capability to adapt to the environment, and are thus time-related. The transition zone comes to an end when the luminance of the zone is equal to 3 times that of the interior level.
4. Interior zone
This inner zone is located between the transition zone and the exit zone. The luminance in this zone is vital for an enhanced level of traffic safety inside the tunnel by day. The interior zone is usually the longest stretch of the tunnel. The lighting levels in the zone are connected to the speed and density of traffic.
5. Exit zone
This is the last part of the tunnel where the eyes begin to acclimatize to the outdoor lighting level. The lighting here must not create a big contrast between luminance in the tunnel and the exterior. During the day, the vision of a driver drawing nearer to the exit is affected by the brightness outside of the tunnel.
The human eye can adjust almost instantly from low to high lighting levels. But, the processes that apply when entering the tunnel are not reversed. Reinforced lighting may be needed in some instances. Where lighting contrast is required in front or behind the driver if the exit is not visible, if the exit serves as an entrance, in case of emergency, or when maintenance works are ongoing and one part of a twin tunnel is closed. The maximum length of this zone is 50 meters and the light level must be five times that of the interior zone.