t/LUX Illuminance meter

The requirements for tunnel lighting are determined by the nature of the human eye. The tunnel lighting must be controlled such that users, both during the day and by night, can approach, pass through and exit the tunnel without changing direction or speed with a degree of safety equal to that on the approach road. Especially at daytime the human eye can only adapt slowly to the lower lighting levels in the tunnel. The lighting in the access zone has to be controlled such that drivers can perceive obstacles in the tunnel on time to stop. At night time it is sufficient to provide lighting levels in the tunnel at least equal to those outside the tunnel.

Several international and national guidelines and standard describe how to design and control tunnel lighting:

• CIE 88:2004 Guide for the lighting of road tunnels and underpasses
• CEN Report CR 14380 Lighting applications – Tunnel lighting
• DIN 67524 Beleuchtung von Straßentunneln und Unterführungen (DE)
• RVS 09.02.41 Tunnelausrüstung Lichttechnik Beleuchtung (AT)

The Austrian RVS for instance describes a reduction of the lighting level in the interior zone based on illuminance levels that prevail in front of the portal.

The illuminance meter measures the illuminance hemispheric. The measured value describes the luminous flux which impacts on the transparent hemisphere of the sensor.

If approach roads are unlit the lighting in the interior zone according to traffic and day time is to be reduced according to the following table. The reduction factor k_red is to be applied to the calculated nominal luminance L_in in the interior zone.