The aim of road tunnel lighting is to ensure that users can approach, pass through, and exit the tunnel with a similar degree of safety to the approach road.
The requirements, limits and design procedures described in current tunnel lighting regulations are based on installations that use HID lamps"
The principal characteristics that determine the quality of road tunnel lighting are the average luminances and uniformities on the road surface and the lower parts of the walls; the control of glare that can impede drivers’ vision; and the avoidance of critical flicker frequencies.
As technology changes, the design of tunnel lighting needs to change too. The requirements, limits and design procedures described in current tunnel lighting regulations are based on installations that mainly use high-pressure discharge lamps. With the introduction of LED-based tunnel luminaires, it will not only be possible to design highly energy-efficient installations, but also to create arrangements that can produce optimised luminance distributions throughout the tunnel.
But due to very pronounced luminous intensity distributions of LED luminaires there is the risk that the visual impression of the luminance distribution on the road in front of a vehicle does not correspond well with the determined values of the lighting criteria obtained by traditional design methods. To overcome these discrepancies it is necessary to extend the current luminance concept and apply an additional angle of observation. This requires knowledge of the reflection characteristics of the surfaces for different angles of observation.
To work out the expected uniformities at the design stage, the calculation grid you need to use is about three times denser than the usual grid. The assumption of a different angle of observation also has an impact on the estimated veiling luminances and the resulting threshold increments in road tunnel lighting. On top of this, glare from LED luminaires has to be considered differently for different tunnel users.
Axel Stockmar is co-author of the CIE’s tunnel and underpass lighting guide, and chairman of the working group that is revising the German DIN standard on tunnel lighting. He’ll be giving the keynote presentation at our first Road Tunnel Lighting conference in Barcelona on 8-9 October. The event is free for specifiers, tunnel operators and consultants working in the field. To register, visit www.tunnellightingconference.com