Entering and exiting a tunnel is much easier and safer with appropriate tunnel lighting. Good lighting is necessary to help drivers to easily adjust their vision from natural light to tunnel light.
What is Tunnel Lighting?
Tunnel lighting is very common inside a tunnel which differs from the brightness outside. It has a lower brightness level compared to outside lighting. The level of light varies on how the driver’s eyes can easily adapt to changes upon entering a tunnel.
40-meter Length Rule
Straight level tunnel meets the 40-meter length rule on which everything is set into consideration, including the lighting requirement.
Daylight can enter on up to 15-meters of the tunnel. The access zone should be visible with the help of daylight to see the road ahead of time.
The required height is 200-centimeter to accommodate any types of vehicles, therefore, also affecting the lighting level.
The remaining 25-meters is the inside length of the tunnel with gradual luminance lighting design. Other tunnels may exceed from 25-meters.
Design and Requirements for Tunnel Lighting
Standard tunnel lighting is divided into zones to help the driver’s eyes adapt to changes. Each zone requires a particular luminance level to keep the driver safe in passing through the tunnel. There are five zones in total, including:
Access Zone
Going towards the tunnel is like confronting a black hole, which could be dangerous. Drivers must see clearly into the tunnel ahead of time to prevent any obstacles if there are any. The lighting on this part of the tunnel should help the eyes to adapt from the outside light.
Threshold Zone
This is the first zone of the tunnel on which requires special lighting different from daylight. In this zone, drivers should maintain their visual reliability to see any obstacle. Adapting into the zone’s luminance level would result in a time lag on the human’s eyes, and it is normal.
They say objects within 20cm x 20cm dimensions could be visible from the threshold zone at 100-meters distance.
The luminance level for the threshold zone is 100-percent in the first half and reduces to 40-percent towards the end of the zone.
Transition Zone
Next to the threshold zone is the transition zone on which adaptation to luminance becomes easier to human eyes. The reason is that in the previous zone the vision already starts to adapt.
The luminance level will gradually reduce in a ratio not exceeding from 3:1. It helps the driver’s eyes to adapt to lower lighting levels.
The transition zone’s length depends on the length from tunnel entrance toward the interior zone level, as it is the longest distance inside the tunnel.
Interior Zone
The Interior zone is simply after the transition zone up to the beginning of the exit zone. There is no need to consider eye adaptation here unlike the previous zones. Its luminance level is fairly high compared to road lighting to quickly correct an error.
The level of light considers the tunnel’s use. The Interior zone has scheduled lighting for daytime and nighttime. Nighttime lighting levels should be higher than in the daytime.
Another thing to consider is when there is a loss of visibility due to dust and smoke, a high lighting level is essential.
Exit Zone
The exit zone is totally different from the access zone of the tunnel in terms of luminance level. It is five times compared to the last zone. However, eyes adapt quickler to the increasing lighting level than decreasing levels.
Upon leaving the tunnel, drivers should still be extra careful, though obstacles could be seen clearly at the bright exit.
Exiting the tunnel at night is similar to entering a black hole. For this reason, road lighting must be present to light up to 300-meters distance from the exit zone.
Other Design Criteria
Apart from standard tunnel lighting, experts’ judgment in planning the lighting system is necessary. A lot of studies should be conducted in enabling tunnel lighting for the safety of all road takers.
One is the visual task that relates to the adaptation status of the human eyes. Also, consider scheduling for tunnel lighting. Daytime lighting could differ from night lighting in certain ways, like the luminous level. These factors will lessen possible accidents inside a tunnel, of course, with careful driving skills.
Final Words
Overall, the contrasting light of the outside road and the tunnel makes tunnel lighting a necessity.The different zones inside the tunnel must be built with the correct level of light for a safe journey.