The requirements for tunnel lighting are determined by the nature of the human eye. How well the eye recognises vehicles and other obstacles in a tunnel depends on the lighting and visibility as well as the reflexion characteristics of the road surface and the tunnel walls. Tunnel lighting needs to be adapted to these environmental conditions.
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 the lighting of a tunnel entrance should be adequate to avoid the “black hole effect” when a driver enters the tunnel.
Luminance is the measure representing what a human being perceives as brightness and as such is the main control variable for the tunnel lighting.
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)
If a measurement of luminaces is indicated luminance meters are used in front of the portal and where required also inside the tunnel.
The luminance photometer comes with a zoom lens that is focussed to measure the relevant area. Light from this area through the lens is directed to the photo element detecting its intensity. The integrated evaluation unit then calculates the luminance and provides it through the analogue output(s).
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t/LUM-A Luminance meter
- Zoom lens to adjust the focus areas
- Sensor with V(λ) filter and silicon photo element
- Temperature compensated and long term stable amplifier for the photoelectric current using live zero
- Heated housing with protection class IP65 either made of polycarbonate or stainless steel 1.4571
- Electronically controlled heating and temperature monitoring
- Mounting flange to adjust horizontal and vertical angle
- Fault indication by relay isolated contact (NC)
- Optional second output channel for increased resolution at low lighting levels
- Surge protection
Mounting locations of the luminance meters
Luminance meter L20
The luminance meter is mounted in front of the portal in stopping distance. It measures the average luminance of the visual field of the driver with an angle of view of 20°. If the luminance meter is not mounted in stopping distance from the portal the angle of view can be adjusted by the zoom lens.
Luminance meter Lth
The luminance meter is mounted on the tunnel wall and aligned on the lane. It measures the luminance Lth in the first part of the threshold zone.
Luminance meter Lin
The luminance meter is mounted on the tunnel wall and aligned on the lane. It measures the luminance Lin in the interior zone.