Illuminance measurement

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.

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t/LUX Illuminance meter

  • Photometer to measure the illuminance at the mounting point of the sensor
  • Cosine correction
  • V(λ) adaptation
  • Delivered ready for operation
  • Shock proof IP65 housing
  • Optional IP65 heated housing
  • Sensor zur Montage am Ort der Messung
  • Anschluss wahlweise direkt an Tunnelleittechnik oder an abgesetztes Auswertegerät
  • Specifically designed for application in and in front of tunnels
  • Customisable measuring range
  • Resistant against corrosion, UV, oil and acid
Technical Specifications
Illuminance measurement
Measured value Illuminance
Measuring range Customisable, typically 0 .. 200 lx
Accuracy ± 3 % (5 .. 200 lx)
± 6 % (at 1 lx)
not defined for values below 1 lx
Zero drift 0.02 lx / °C
20 °C
Spectral range of photosensitivity Adapted by V-Lambda Filter
V(λ) ≥ 80% between 490 nm and 630 nm
Half ellipse, Erel = 0.8 at ± 35°
Illuminance sensor
Model t/LUX
Power supply 24 VDC via current loop
Material Glass bead reinforced polyamide (PA 6 30% GK)
Protection class IP 65
Dimensions 64 x 98 x 34 mm
Weight 300 g
Illuminance sensor heated version
Sensor t/LUX-H
Power supply 230 VAC (other voltages on request)
Heating 100 W (controlled by thermostat)
Material Glass fibre reinforced polyester, RAL 7035 or
Stainless steel 1.4571 (AISI 316Ti) (optionally)
Protection class IP 65
Dimensions 250 x 300 x 140 mm
Weight 4.5 kg
Analogue output 1 x 4 – 20 mA, 2-wire, passive
Electrical standards 2006/95/EC Low Voltage Directive (LVD)
2004/108/EC Electromagnetic compatibility (EMC)
IEC 61326-1:2012
IEC 61010-1:2010
Tunnel safety standards AT: RVS 09.02.41
DE: RABT 2006, DIN 67542-2


Product info DE (PDF, 325 kB)
Product info EN (PDF, 325 kB)


Lighting of interior zone at night time according RVS 09.02.41

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 kred is to be applied to the calculated nominal luminance Lin in the interior zone.

Illuminance EA Day time Traffic Reduction factor kred
> 100 lx 1.00
≤ 100 lx 04:00 – 08:00
16:00 – 22:00
22:00 – 04:00 > 100 Kfz/h 0.25
≤ 100 Kfz/h 0.125