Tunnel Lighting – For comfort, safety and visual performance

Tunnel lighting requirements differ from road lighting in that they must address sudden changes in brightness over critical lengths, while road lighting mainly focuses on night visibility. In the majority of tunnels, the natural penetration of light does not allow satisfactory visibility for users. It is therefore necessary to install artificial lighting to improve visibility and comfort.

The International Commission on Illumination (CIE) standards requires that the amount of light within a tunnel is dependent on the level of light outside and on the point inside the tunnel at which visual adaptation of the user must occur. There are five key areas to consider while illuminating the tunnel. The Access Zone which is not within the tunnel itself but the stretch leading to its entrance. From this zone, drivers must be able to see into the tunnel in order to detect possible obstacles and to drive into it without reducing speed. The second is the Threshold zone which is equal in length to the ‘stopping distance’. In the third Transition zone, luminance is reduced progressively to reach the Interior or fourth zone which is often the longest stretch of the tunnel. The fifth and final is the Exit zone and, in this zone, during the day, the vision of a driver approaching the exit is influenced by the brightness outside the tunnel.

Motorists approaching a tunnel entrance experience what is known as the “black hole effect”. This is because luminance levels inside the tunnel are much lower than those outside and the eyes have difficulty adapting to the sudden difference. To alleviate this effect, a higher, “reinforced” level of lighting is at the tunnel entrance. This will ensure that drivers can see objects within the correct stopping distance before entering the tunnel. It will also help to prevent them from slowing down, which is important to maintain optimal traffic flow. In order to enable drivers’ eyes to adapt from the entrance zone lighting to the interior zone lighting, the entrance lighting level is gradually reduced as drivers move along the tunnel. Once drivers have adapted to the lower luminance levels in the tunnel, sufficient lighting is needed in the interior zone for safe passage.

In terms of functionalities, the lighting installation must allow for normal lighting that provides appropriate visibility for users during both day and night, safety lighting that provides minimum visibility for users to enable them to leave the tunnel in their vehicles in case of power outage and evacuation lighting to guide tunnel users on foot in the event of an emergency.

Traveling through tunnels can be both a thrilling experience and a visual treat. Sydney’s nine-kilometre long NorthConnex motorway tunnel boasts artwork, changing visual displays and unique lighting features to keep drivers engaged as they travel. The lighting displays were installed after extensive research to help keep drivers alert and engaged and the tunnel is equipped with innovative, advanced LED lighting to ensure motorists can safely transition from bright daylight to the darker interior tunnel section.

Content sourced from articles on tunnel lighting